Add .jshintrc and update admin.js to (better) match WP JS coding standards.

Mainly consists of adding in spaces inside ( ) and [ ], removing spaces before :, unquoting simple object keys, etc.
Use key notation for import property, since import is a reserved word in ES3.
Fix extra comma in .jshintrc that was stopping it from working.

Remove the globals declaration from inside the file, that was only kept as .jshintrc didn't appear to be working.
Merge pull request #15 from GaryJones/feature/js-cs

Update JS to match coding standards