Blender Git Loki

GP UI - 2D/3D Split: Split out the "Create Shapes" and "DrawingToolsPanel" into separate classes

The 3D/GP Object only used part of the old "DrawingToolsPanel" to
draw the "Shapes" panel, going so far as to use an empty label +
custom draw header function to dynamically change the label.

This commit properly fixes the code here by separating out the code for
the two use cases:
* The GP object case is now handled by a dedicated "GreasePencilCreateShapesPanel"
that only does the "Shapes" stuff
* I've reverted the other case back to the master version, as this is more
suitable for use by all the other 2D editors