[Review Only] Use CodeInspection API

This is based off of master, but includes `mark/fixes-linter-reporter` and `mark/dark-widget` because I wanted that code to be in here before I started work on the CodeInspection API changes.

I'll create a new PR once we merge both `mark/fixes-linter-reporter` and `mark/dark-widget` in some form into Interactive Linter, to make this have a less odd commit log.

TODO/Notes:
  - This does not underline in code, as Brackets doesn't provide a token, only the linter-reported start pos.
     - I don't know how feasible it would be to create tokens for (theoretically) any linter out there.
  - This PR takes the CodeInspection API `inspectFile` and then does all of our handling on the results.

Things that are not yet implemented/Regressions:
  - Fatal error checking
  - Error vs. Warning messages
  - Better integration into the panel when only one linter is present
    - Make it display like Brackets does, where the panel title has the linter name and the errors are displayed without sectioning.
  - (?) Don't disable the default JSLint of Brackets
  - Anything else?