Simple to use editor component (non-collab for now)

This should be the future of the editor component(s). A simple API for 3rd-party WebODF editor interested, hiding all the internal complexity, so allowing us to throw things around as we need, without breaking things too much for that 3rd-party.

`make product-wodotexteditor` will create a zip file with everything needed for the editor component. Unzipping that file and following the HOWTO should make people happy. So far I successfully managed to follow my own text in there and get happy a little :)

Fixes #295 
Partially solved #195 (besides the compilation).
The more common name for such an action is "join". I suggest `joinSession`.