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:
- [x] immediately dismiss message on:
    * when displaying another inline editor error
    * on scroll
    * change editors
    * selection change
    * edit page
- [x] scroll cursor into view
- [x] unit tests
- [x] determine conflicts with other floating thingies
    * Quick View
    * other Quick Edit or Quick Docs widget
    * main menus (HTML & native)
    * context menu
    * dropdowns (New Rule?)
- [x] UX review
- [ ] string review
- [ ] any InlineColorEditor error cases that can be handled?
- [ ] code review
- [ ] rebase
- [ ] update quick edit API documentation