[FEATURE] New version of color button (QgsColorButtonV2) based off

QToolButton. Features:
- context menu items have been moved to the attached menu button
- new gui widget QgsColorSwatchGrid, which displays a grid of colors
- new class for QgsColorScheme, which generates colors to show in a
  color swatch grid
- new class QgsColorSchemeRegistry, with a global instance containing
  default color schemes. QgsColorButtonV2 accepts a color scheme
  registry, to control which schemes to show in the popup menu as
  color swatch grids.
- color button can have a default color
- color button can also be quickly set to a totally transparent color
- c++ and python unit tests for all core components

python/core/core.sip

@@ -16,6 +16,8 @@
 %Include qgsattributeaction.sip
 %Include qgsbrowsermodel.sip
 %Include qgsclipper.sip
+%Include qgscolorscheme.sip
+%Include qgscolorschemeregistry.sip
 %Include qgscontexthelp.sip
 %Include qgscoordinatereferencesystem.sip
 %Include qgscoordinatetransform.sip

python/core/qgscolorscheme.sip

@@ -0,0 +1,70 @@
+/**List of colors paired with a friendly display name identifying the color*/
+typedef QList< QPair< QColor, QString > > QgsNamedColorList;
+
+/** \ingroup core
+ * \class QgsColorScheme
+ * \brief Abstract base class for color schemes
+ *
+ * A color scheme for display in QgsColorButtonV2. Color schemes return lists
+ * of colors with an optional associated color name. The colors returned
+ * can be generated using an optional base color.
+ * \note Added in version 2.5
+ */
+class QgsColorScheme
+{
+%TypeHeaderCode
+#include <qgscolorscheme.h>
+%End
+
+    public:
+
+    QgsColorScheme();
+
+    virtual ~QgsColorScheme();
+
+    /**Gets the name for the color scheme
+     * @returns color scheme name
+    */
+    virtual QString schemeName() const = 0;
+
+    /**Gets a list of colors from the scheme. The colors can optionally
+     * be generated using the supplied context and base color.
+     * @param context string specifiying an optional context for the returned
+     * colors. For instance, a "recent colors" scheme may filter returned colors
+     * by context so that colors used only in a "composer" context are returned.
+     * @param baseColor base color for the scheme's colors. Some color schemes
+     * may take advantage of this to filter or modify their returned colors
+     * to colors related to the base color.
+     * @returns a list of QPairs of color and color name
+    */
+    virtual QgsNamedColorList fetchColors( const QString context = QString(),
+        const QColor baseColor = QColor() ) = 0;
+
+    virtual QgsColorScheme* clone() const = 0 /Factory/;
+
+}; // class QgsColorScheme
+
+/** \ingroup core
+ * \class QgsRecentColorScheme
+ * \brief A color scheme which contains the most recently used colors.
+ * \note Added in version 2.5
+ */
+class QgsRecentColorScheme : QgsColorScheme
+{
+%TypeHeaderCode
+#include <qgscolorscheme.h>
+%End
+
+  public:
+
+    QgsRecentColorScheme();
+
+    virtual ~QgsRecentColorScheme();
+
+    virtual QString schemeName() const;
+
+    virtual QgsNamedColorList fetchColors( const QString context = QString(),
+        const QColor baseColor = QColor() );
+
+    QgsColorScheme* clone() const /Factory/;
+}; // class QgsRecentColorScheme

python/core/qgscolorschemeregistry.sip

@@ -0,0 +1,59 @@
+
+/** \ingroup core
+ * \class QgsColorSchemeRegistry
+ * \brief Registry of color schemes
+ *
+ * A registry of QgsColorScheme color schemes. This class can be created directly, or
+ * accessed via a global instance.
+ * \note Added in version 2.5
+ */
+class QgsColorSchemeRegistry
+{
+%TypeHeaderCode
+#include <qgscolorschemeregistry.h>
+%End
+	public:
+
+    /**Returns the global instance pointer, creating the object on the first call.
+     */
+    static QgsColorSchemeRegistry * instance();
+
+    /**Constructor for an empty color scheme registry
+     */
+    QgsColorSchemeRegistry();
+
+    virtual ~QgsColorSchemeRegistry();
+
+    /**Adds all color schemes from the global instance to this color scheme.
+     * @see addDefaultSchemes
+     * @see addColorScheme
+     */
+    void populateFromInstance();
+
+    /**Adds all default color schemes to this color scheme.
+     * @see populateFromInstance
+     * @see addColorScheme
+     */
+    void addDefaultSchemes();
+
+    /**Adds a color scheme to the registry. Ownership of the scheme is transferred
+     * to the registry.
+     * @param scheme color scheme to add
+     * @see populateFromInstance
+     * @see removeColorScheme
+    */
+    void addColorScheme( QgsColorScheme* scheme /Transfer/ );
+
+    /**Removes all matching color schemes from the registry
+     * @param scheme color scheme to remove
+     * @returns true if scheme was found and removed
+     * @see addColorScheme
+    */
+    bool removeColorScheme( QgsColorScheme* scheme );
+
+    /**Returns all color schemes in the registry
+     * @returns list of color schemes
+    */
+    QList<QgsColorScheme *> schemes() const;
+
+}; // class QgsColorSchemeRegistry

python/gui/gui.sip

@@ -33,7 +33,9 @@
 %Include qgscodeeditorcss.sip
 %End
 %Include qgscolorbutton.sip
+%Include qgscolorbuttonv2.sip
 %Include qgscolordialog.sip
+%Include qgscolorswatchgrid.sip
 %Include qgscomposerview.sip
 %Include qgscredentialdialog.sip
 %Include qgsdetaileditemdata.sip