[Review Only] Display Inline Editor Errors

This has been implemented using proposal outlined [here](https://groups.google.com/forum/?fromgroups#!topic/brackets-dev/APEzunRwfrE).

The Quick Docs Feature uses the same mechanism, so it is also supported.

Code handles errors for the CSS, JS, and InlineTimingFunction Inline Editors. Are there any cases that could be handled for the InlineColorEditor? Any other Inline Editors?

TODO:
- [ ] UX review
- [ ] InlineColorEditor
- [ ] determine cases to immediately dismiss message
    * when displaying another inline editor error (done)
    * on scroll?
    * change editors?
    * click in page?
    * typing?
- [ ] determine conflicts with other floating thingies
    * Quick View
    * main menus (HTML & native)
    * context menu
    * dropdowns (New Rule?)
- [ ] unit tests
- [ ] code review
- [ ] rebase