Remove Vector2.tmp() and its variations (.tmp{1,2,3})

Down with public static mutable objects.  Up with private static mutable objects ... I guess.
Remove Vector2.tmp usage from PathTest and StageTest
Add a static scratch vector in pax-britannica's Ship.java
Replace Vector2.tmp usage with local static scratch variables throughout scene2d.

This breaks the API since Vector2.tmp* were all public.
Merge pull request #256 from bitiotic/squash-vector2-tmp

Remove Vector2.tmp() and its variations (.tmp{1,2,3})