Rich editor addition and configuration

What this branch does

- Removes TinyMCE
- Adds Rich Editor
- Configures Paperclip support for adding fmages in S3 on the fly
- Configures appearance of the editor in active admin
- Configures the editor toolbars in active admin
- More importantly, works in Heroku

What this branch does NOT

- For now, there is limited support for predefined custom styles [asset pipeline not compiling the app/stylesheets/rich/editor.css]
- Upload images to the same path as galleries
- Upload images locally

These issues must be related to the Paperclip paths configurations

What is left to be done:

- Decide which Active Admin fields will have the Rich editor as their main editor.

Possibly closes #33 and #34