Merge GOWN.shapes with PIXI.core.math.shapes

[brean]

There are already shapes defined in PIXI. We can of course extend them but it sounds like a good idea to remove our shapes and merge with PIXI.

see https://github.com/pixijs/pixi.js/tree/dev/src/core/math/shapes

[FlorianLudwig]

done in merge request #93

[brean]

reponed: its not done!