Breaks: Document id same as attribute key

A document with an id that is the same as an attribute id can't be edited - e. g. create a document with the id 'title' where the document contains an attribute 'title'. When going into edit mode, it will appear corrupted depending on the attribute level editors used in that document.

I have pushed a fix that breaks backwards compatibility:
https://github.com/developmentseed/bones-document/commit/744b12633a76dea4c516363bee60c9e407385268

This fix breaks backwards compatibility. Existing templates need to be updated and attribute keys need to be prefixed with `editable-` so that for instance the class `title` becomes `editable-title`.

Needs review.