[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.

This still works with the current CodeInspection API (adobe/brackets@2333b85790518b1b7b84b1511bd83f77375aed53)

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.
  - The CodeInspection API does not put Synchronous linters into workers, so that is a theoretical performance regression.
  - This makes the linter panel a mix of custom/Brackets code, since I don't copy the CSS from Brackets for the lint panel.
  - We could use `inspectFile` once (probably in `setDocument`) and then pull the providers out of that, doing provider management ourselves.
    - If we did this, a fake file with the same path ending might be a good idea, as it would reduce time spent to get the provider results. This fake file would be empty in terms of contents.
  - (?) Don't disable the default JSLint of Brackets

**Regressions:**
  - Fatal error checking
     - TODO: Check if Brackets 'aborted' flag on results actually is used by lint provider extensions. If so, this is done.
  - Error vs. Warning messages (everything is marked as a warning)
      - Different linters/providers have different concepts. CodeInspection.Type is not enough; it isn't descriptive enough, nor does it seem to be used widely by provider extensions.
  - 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.
  - Anything else?

**What this deprecates:**
  - `pluginWorker.js`
  - `pluginLoader.js`
  - `pluginManager.js`
  - `linterSettings.js`
  - `plugins/*`

Note: I'll update this main comment as I think of new things, and mark things as `Resolved` when (and if?) they get resolved.
This calculates the total amount of error messages given by all providers.