Integrate ACE editor

This pull request is for [task 62](https://assemblymade.com/buckets/wips/62).
It's still a work in progress; not ready to be merged yet!

TODOS:

- [x] Ace should *not* get built into either buckets.js or vendor.js, but rather it should be loaded separately in the TemplateEditor with `modernizr.load`.
- [x] Make it so that changes to the ace editor field actually save when you
      click the "save" button
- [x] Add syntax highlighting for web languages