Graphical user interface landed

Finally after several years of development a graphical user interface landed. It's far form complete but ready for a first review.

Unlike the other graphical sieve editors, it works like a visual code generator. It just abstracts syntax and basic grammar. Thus grammar is not limited, so it's possible to have arbitrarily nested if statements.

The interface relies on drag&drop. To create Elements just drag them from the sidebar and drop it a the desired position. Deleting is even more simple. Drag the element into the trash, and it's gone including all nested elements. In order to move elements drag them, indicators will guide you where it's safe to drop. To edit an element just click on it.

Until now the interface supports basic Sieve supports RFC5228, RFC5232 and RFC5429.

There is still much work left. The user interface is fully functional but need polishing to look nice.

Feedback is welcome. Just post it to the mailinglist sieve(at)mozdev.org or directly to me schmid-thomas(at)gmx.net