Update to work in Rails 4 non-fingerprinted environment.

We do this by cheating. Instead of do some crazy mojo to get ckeditor talking
to the fingerprinted versions of the assets we simply create non-fingerprinted
versions like it used to work in Rails 3.

Since this is not what a developer might expect happen we limit our cheat
to only assets produced by ckeditor.

Our task that does this is named assets:precompile. This way our functionality
is appended to the standard funtionality. This will allow it to work in
environments like Heroku where the name of the task that is run to generate
the assets cannot be changed.

The end result is that everything should work out-of-the-box, not affect
anything bug ckeditor and requires minimal changes to this gem.

This fixes issue #18.
Merge pull request #21 from eric1234/master

Update to work in Rails 4 non-fingerprinted environment.