add import button to context menu
Merge branch 'Feature-CustomShapes' of https://github.com/PowerPointLabs/repo into Feature-CustomShapes

Conflicts:
	PowerPointLabs/PowerPointLabs/CustomShapePane.Designer.cs
first version of import
multiple select dragging effect
correct dragging effect
remove rename slide feature
refactor selection rectangle code
#572 half done, need to be tested