Scintilla Editor

This adds a new code editor based on QScintilla2.
More info:
* https://github.com/openscad/openscad/wiki/ScintillaEditor-TODO-list
* https://github.com/openscad/openscad/wiki/GSoC-2014-Project-Timeline

TODO before merge:
 - [ ] Build system for QScintilla2 on Mac
 - [ ] Build system for QScintilla2 on Linux
 - [ ] Build system for QScintilla2 on Windows
 - [ ] Test snapshot build on Mac
 - [ ] Test snapshot build on Linux
 - [ ] Test snapshot build on Windows