Bug 937431 - [Tooling] make jshint a requirement on pre-commit

https://bugzilla.mozilla.org/show_bug.cgi?id=937431

- Creates a `build/jshint-xfail.list` containing a list of all files currently failing jshint
- Creates a custom reporter `build/jshint-xfail.js` that allows errors within xfail files to be displayed (but not in travis) and not error for `make lint`
- `make lint` now runs `make gjslint hint`
- Moves current `make lint` to `make gjslint` and only runs for files listed in `build/jshint-xfail.list`
- Changes `tools/pre-commit` to run `make gjslint` and `make hint`
    - Adds a message to the pre-commit for each file that is currently xfailed that your commit will touch.