Updates for Snap2D world and script libs, sprite editor bug fixes

Snapdragon2D
-Fixed Sprite editor sometimes not saving polygon data correctly
-Fixed SpriteData not loading local image correctly
-Added menu bar to Sprite editor
-Added save-on-exit check to editor
-Snap2D world collision reworked; now based on polygon intersection
-Updated demos to work with new collision system
-Unfinished progress on SnapScript compiler
2DX-GL
-Added several new utility methods
-Added line intersection computation to GeoUtils
-Added Multimap utility class