Tighten margins and spacing on various docks

Fixes a rendering artefact on OSX toolbars and leaves more
space for content.

Let me know if this looks bad on Windows and I'll ifdef it out

src/app/qgisapp.cpp

@@ -3040,6 +3040,8 @@ void QgisApp::initLayerTreeView()
 
   QVBoxLayout* vboxLayout = new QVBoxLayout;
   vboxLayout->setMargin( 0 );
+  vboxLayout->setContentsMargins( 0, 0, 0, 0 );
+  vboxLayout->setSpacing( 0 );
   vboxLayout->addWidget( toolbar );
   vboxLayout->addWidget( mLayerTreeView );
 

src/app/qgsattributetabledialog.cpp

@@ -98,6 +98,10 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *theLayer, QWid
 
   setAttribute( Qt::WA_DeleteOnClose );
 
+  layout()->setMargin( 0 );
+  layout()->setContentsMargins( 0, 0, 0, 0 );
+  static_cast< QGridLayout* >( layout() )->setVerticalSpacing( 0 );
+
   QSettings settings;
 
   int size = settings.value( "/IconSize", 16 ).toInt();

src/app/qgsbookmarks.cpp

@@ -41,6 +41,10 @@ QgsBookmarks::QgsBookmarks( QWidget *parent )
   setupUi( this );
   restorePosition();
 
+  bookmarksDockContents->layout()->setMargin( 0 );
+  bookmarksDockContents->layout()->setContentsMargins( 0, 0, 0, 0 );
+  static_cast< QGridLayout* >( bookmarksDockContents->layout() )->setVerticalSpacing( 0 );
+
   QToolButton* btnImpExp = new QToolButton;
   btnImpExp->setAutoRaise( true );
   btnImpExp->setToolTip( tr( "Import/Export Bookmarks" ) );

src/app/qgsbrowserdockwidget.cpp

@@ -270,6 +270,10 @@ QgsBrowserDockWidget::QgsBrowserDockWidget( const QString& name, QWidget * paren
 {
   setupUi( this );
 
+  mContents->layout()->setContentsMargins( 0, 0, 0, 0 );
+  mContents->layout()->setMargin( 0 );
+  static_cast< QVBoxLayout* >( mContents->layout() )->setSpacing( 0 );
+
   setWindowTitle( name );
 
   mBrowserView = new QgsDockBrowserTreeView( this );