Adding save button option.

Moved the text area and preview panes out into it's own class.
Fixed up styling

After the refactor the styling for the textarea and the preview pane
were more than a little broken.
Moved footer into its own class.

It now adds to the body correctly.
Fixed changed event

Forgot to rewire up the change event when moving the content out into
it's own class.
Footer is now API complete

Added the methods and events to the footer for the editor to tie into.
Footer disabling/enabling

Tied the footer buttons disabling and enabling when the text changes.
Made footer buttons functional

When the buttons in the footer are clicked they will now update the base
editor class.
Updated readme

Added documentation on the save flag.