Clicking a shape button works only for the default shape,
not for the last used one.

Steps to reproduce:
1) Click on the drop-down arrow of one of the shape buttons,
   and select a shape. Notice that the button icon updates
   with the last selected shape.
2) Click on another button.
3) Click on the first button, and try to draw something.
   The button doesn't work anymore. Only opening the sub
   toolbar and selecting the shape there will work.

The problem is in ToolboxController::execute that requires
the command to be in the listener map, but we didn't
register sub commands (like .uno:SymbolShapes.sun).
Instead of doing that, we'll try some generic solution.
(Note that calling the corresponding method from
SvxTbxCtlCustomShapes like we do in other methods here
won't work, because ChartController::queryDispatch checks
for the "_self" target, but SfxToolBoxControl::Dispatch
doesn't provide it.)

Change-Id: I5be3dfd3ee3ca9ab9d8080929173dbe5984f61a0