Changed to Rails 4

Refer to #74 and #81.

Update to Rails 4 done. Here are the steps I went through : 

- Modified the `Gemfile`. Removed the assets group (Rails 4 doesn't use it), and changed the rails version to 4. I then ran `bundle update` and found out that I had to upgrade the versions for sass-rails and coffee-rails too. 
- Changed *match* in `config/routes.rb` to *get*.
- Added the `protected_attributes` gem. This is temporary, and just to ease the transition to Rails 4. Ideally, this gem should be removed and we should make use of strong parameters. If this pull request is merged, I'll open an issue for the same. 
- ~~Removed Turbolinks. Turbolinks was causing a problem with the drawing application. I've mentioned more details at #81~~ Turbolinks is included now, refer to #87