JSHint configuration for keeping code clean

* Created strict moded `.jshintrc` file with code quality rules
* Modified grunt task for to fit our app:
  * `grunt jshint:all` - checks whole application
  * `grunt jshint:frontend` - checks angular part of application
  * `grunt jshint:backend` - checks our models, routes, etc.
* Corrected all issues pointed by JSHint.
This pull request references to #34