Merge pull request #219 from nazgee/for-nicolas-scissor-fix

ClipEntities can now be nested.
Minor changes in GLScissorStack.
Minor change.
Added methods to easily convert from/to parent Entity coordinates.
Added preliminary versions of LineLoop and LineStrip.
Added MathUtils.factorial.
Added BezierCurveUtils.
Added SpriteBatch.getCapacity(). Minor changes.
Minor changes.
Optimization in BezierCurveUtils.
BezierCurveUtils can now also calculate the curvature of a bezier curve at any point.
Add IEntity::get|setRorationOffset

This change affects only how Entities are drawn. It does not modify
values returned by get|setRotation.

This is wanted since some external tools assume that Sprites' textures
can be rotated regardless of the whole Sprite's rotation 0.

It could be fixed by intoducing custom classes but this solution is much more
generic. It also seems quite safe.
Merge branch 'for-nicolas-rotationoffset' of github.com:nazgee/AndEngine into nazgee