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).
Okay, if you ask for :) Hardcoded to pullbox, as there are no other backends known yet which use the same abstractions as pullbox does (thus the recently introduced SessionBackend). But if you want that, no problem :)
Done.