Toggle widgets and behaviours

This is a pull request for establishing a way to toggle some of the most prominent features of ACE, namely collapsing/expanding code blocks (widgets) and auto-pairing grouping characters (behaviours). I'm not sure why the changes from rlerdorf's commit are showing up as though they are new changes. I think the one difference in my version is that there is a newline at the end of the file. I can't say how that happened...

The clickable boxes I made to toggle these features are just something to suggest how to go about setting up such an interface. Perhaps you'd prefer a different visual approach. I think it would be great to let the user invoke other features of the ACE editor as well, especially allowing them to choose a theme, but I think users would really appreciate turning just these features on and off. Please let me know what you think.