Pivot: support align (top/bottom/left/right) to self

[eFe-Munoz]

My proposal is to add in the animation palette an option for the pivot to be aligned with respect to the shape.

This way with one click you can get the pivot to be placed for example centered and at the base of the object in two clicks.

This way of aligning pivots is very useful for animation, if you don't have to do it by hand and it is not very effective.

[rodlie]

pivot to be aligned with respect to the shape

Please specify what should happen.

[rodlie]

#142 (comment)

@eFe-Munoz Ok, understand what you want.