Turn most of moc into a static libmoc, for reuse in scxml

QtScXml contains a copy of the moc source code, with a few patches on top. Since many contributors are unaware of the copy, they change moc without copying their changes over to the scxml clone and thus it's left up to the maintainer of scxml to sync the two every now and then.

If moc was turned into a static library, with a more-or-less trivial main() remaining as moc-the-tool, the scxml tool could link to it, with its own version of main(), perhaps equally trivial.