We can use the `config.authorize_with` option, so we don't need to copy
the controller in order to load and authorize resource.
Besides, only administrators can upload images, so we don't need to
track the image's user id.
Just so we can navigate throught git history faster:
* Introduced in 345e34d to avoid precompiling all CKEditor assets.
* Modified in 54c82a5 to avoid compiling assets during tests.
* Overwritten by `rails g ckeditor:install` in c0d6c0b.
As stated in #1196, compiling everything related to CKEditor made
compilations slower. However, not compiling any plugins meant Travis had
to compile them while running a test. It often resulted in a test
failing because the time Travis took to compile the plugins the
application uses exceeded Capybara's wait time.
