Rename jshint_conf.js to .jshintrc

By doing this sublime text and webstorm will start reporting jshint errors inside the editor.

For Sublime Text:
- Install package SublimeLinter
- Install package SublimeLinter - jshint
- From Terminal `npm install -g jshint`

For WebStorm
- Preference -> JSHint
- Make sure `Enable` and `Use config files` are selected
Merge pull request #6959 from guardian/jshintrc

Rename jshint_conf.js to .jshintrc