Roundcube plugin to store contacts/calendar into maildir

GOAL: Store contacts and calendar information into Maildir, this way it will be protected by trees encryption. MUA's can have plugins to read the info from there, such as SyncKolab.

There is previous work on this by Kolab, but it needs to be adapted to our system as we are not running the Kolab system. https://git.kolab.org/