[IMP] add method to the summernote lib to clean the dom

This branch is not made to be merged directly.

Take what you need and hope that this will be useful and that we can have as many of these features in your next release.

[summernote_ext.js]

I worked with the distributed file because we use in Odoo and wanted a scalable behavior adapted to our needs. The new methods allow to have the same behavior on chrome / firefox / ie and have a clean dom without crappy span or otherwise.

[summernote.js]

In the base file with the line "this.*****" have been added to allow extension of the lib and change behavior based on page or api charged. Some lines are marked as patches.
(to find modification: search with odoo)