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.
New plugin that allows the handling of an Amavisd-new SQL quarantine.
NB: a DB connections manager has been added inside the lib because
Django does not support multiple connections at the same time. The
main consequence is that we don't use an ORM and that we have to
rewrite a small wrapper that supports several DB (mysql, postgresql, etc.).
Adding a dependancy to an existing ORM module (like SQLalchemy) is
heavy, we don't want that for now.
tonio