Code editor using QScintilla

This pull request adds a new qgscodeeditor object which can be used as a base for all text editors that need good editor support and syntax highlighting, project macros, expression widget, html editors, etc

Original Code by Salvatore Larosa

Tested on Windows.  Needs testing on other platforms.

![image](https://cloud.githubusercontent.com/assets/381660/3594260/21d26986-0c98-11e4-9d6c-491af2b68c1f.png)

Maybe leave off _QScintilla2_? Seems like if the editor does not have a specific title, then the user is presented with a text editor, regardless. I don't think users are going to know what QScintilla2 is, so it may confuse them.