Allow plugins to add actions to top level of raster/vector/db/web menus

Provides a way to avoid plugins creating submenus with a single
action - e.g. "DB Manager" -> "DB Manager". It's a violation of
HIG to have a submenu with a single action contained in it.

Author: nyalldawson

src/app/qgisapp.cpp

@@ -10963,6 +10963,9 @@ void QgisApp::removePluginMenu( const QString &name, QAction *action )
 
 QMenu *QgisApp::getDatabaseMenu( const QString &menuName )
 {
+  if ( menuName.isEmpty() )
+    return mDatabaseMenu;
+
   QString cleanedMenuName = menuName;
 #ifdef Q_OS_MAC
   // Mac doesn't have '&' keyboard shortcuts.
@@ -11004,6 +11007,9 @@ QMenu *QgisApp::getDatabaseMenu( const QString &menuName )
 
 QMenu *QgisApp::getRasterMenu( const QString &menuName )
 {
+  if ( menuName.isEmpty() )
+    return mRasterMenu;
+
   QString cleanedMenuName = menuName;
 #ifdef Q_OS_MAC
   // Mac doesn't have '&' keyboard shortcuts.
@@ -11055,6 +11061,9 @@ QMenu *QgisApp::getRasterMenu( const QString &menuName )
 
 QMenu *QgisApp::getVectorMenu( const QString &menuName )
 {
+  if ( menuName.isEmpty() )
+    return mVectorMenu;
+
   QString cleanedMenuName = menuName;
 #ifdef Q_OS_MAC
   // Mac doesn't have '&' keyboard shortcuts.
@@ -11096,6 +11105,9 @@ QMenu *QgisApp::getVectorMenu( const QString &menuName )
 
 QMenu *QgisApp::getWebMenu( const QString &menuName )
 {
+  if ( menuName.isEmpty() )
+    return mWebMenu;
+
   QString cleanedMenuName = menuName;
 #ifdef Q_OS_MAC
   // Mac doesn't have '&' keyboard shortcuts.