Version 0.7.2 - removed dependance on manipulating fabric prototypes

Changed strokeWidth, stroke color and fill color to be set through a separate "state" variable in `drawing-tool.js` rather than being changing the `fabric.<object>.prototype`.

Known issue: free draw width/color will not update when the color/stroke width is changed. DrawingTool needs to start emitting events when those state properties change... to be addressed in an upcoming release.