New methods: Croogo.Wysiwyg.isDirty()|resetDirty()
New method Admin.protectForms()

Protect accidental page refresh causing data loss:

- To protect a form, add 'protected-form' in the class attribute.
- To whitelist elements, add 'data-ignore-elements' containing its selector
Protect some forms from accidental data loss

Closes #410
Merge branch '2.0-dirty-bit' into 2.0