renaming draggablevertices to polygoneditor

... this class will be used as a more general polygon editor thing, so
this reflects this change
Switching to Nape's GeomPolys instead of using shapes and bodies

This allows us to piggyback on loads upon loads of polygon editing
functionality already provided by the GeomPoly class. It also allows us
to use a drawing function different from nape's debug draw, and will
probably be loads cheaper in terms of CPU power
Updated exporting

- moved export function to editorpolygons as it makes more sense
- removed editorsprite's unnecessary subclassing of flxnapesprite
- removed stuff about circle shapes in export - for now