CKEditor support

It can be useful, because image upload feature can be easily added with [ckeditor](https://github.com/galetahub/ckeditor) gem:

gem 'spree_editor', :git => 'git://github.com/secoint/spree_editor.git', :branch => 'ckeditor'
gem 'ckeditor'

rails generate ckeditor:install --orm=active_record --backend=paperclip
rake db:migrate