This is not finished yet. More work than what I expected but the main part is done.
It will need a lot of testing... There is still a bug when activating a new extension
in development mode (ie. with python web server), I think it does not occur behind
a real web server.
Many updates in this commit:
* first work on the webmail plugin, for now only emails listing and folders browsing is supported...
* New login form,
* New graphical layout (still needing improvments)
* code factoring between webmail and quarantine plugins
* etc.
tonio