[Review Only] JS Code Hints: Remember timed out files, notify user

@dangoor 

I pushed this interim branch for you to take a look. This works for some code paths.

TODO:
- [x] bug: `isFileExcludedInternal()` not called on all code paths (cannot repro, maybe confused similar file names)
- [x] implement notification dialog
- [x] don't exclude file currently being edited
- [x] convert pref to project scope?
- [x] remove `console.log()` statements
- [ ] rebase this branch

How about something like this: "JavaScript File Inference Problem" (title). Info:

```
Brackets ran into trouble processing:<br><br>{0}<br><br>This file will no longer be processed for code hints and jump to definition. To turn this back on, open <code>.brackets.json</code> in your project and remove the file from jscodehints.exclusions.
```