Global cleanup

* Add some comments, add `XXX` comments for things to do (meteor
  convention)
* Remove unused `Coupons` collection
* Move all code related to the client configuration in
  ./client/config/
* Add a few more translations and move some strings from the `.js`
  code to the templates
* Fix style (indentation, spaces, etc.)
* Remove some useless `console.log` on the client