It now properly shoves over the email content over DBus, and the
akonadi agent spins up the pEp engine and processes the stuff.
Now we just have to put a bit more logic into it and also make sure
it properly syncs with other pEp users.

The MIME function which generates a string from the struct still
crashes, probably due to an empty string list.

Additionally achieved finally a clean inheritance from DBus::Variants
through separating the Qt from the client class.