Turn 'server' into a gobject

while working on gsettings based keyboard configuration i noticed that i won't be able to do this cleanly if we pass the server around everywhere. Since this is the first thing created it makes sense to have this as a singleton to avoid the overly long a->b->c->server->config (and similar chains).

Once this is in i'll rebase !92 (merged) on top of it (and shift commits around a bit) which will make it possible to get rid of keyboard_create().

@sebastian.krzyszkowiak since this touches lots of places a quick review would be nice .

it contains !96 (merged) but should rebase cleanly on top.