Start of the message (email/news) handling.

The message class for now contains just a pointer to the mime-tree,
meta-data handling is still missing.

There are also a query and a monitor job as well as a self-updating
(flat) message model.

This instroduces a dependency to libkmime, which is GPL. I assume that
linking LGPL code against a GPL-only library is a problem, right? How do
we solve this?

CCMAIL: kde-pim@kde.org

svn path=/trunk/KDE/kdepim/libakonadi/; revision=526069