WIP: Add example code editing and reset functionality

this adds the functionality of editing code shown with the gallery examples and also the ability to reset back the changes.

to test locally, one needs to have the docs served from a server.
reading 'file://' is denied by most browsers.

Simple Solution - "python -m SimpleHTTPServer" in the docs folder
Rename to something like ``EDIT_REVERT_BTN`` for readability