Libraries in trunk

[Nick Schermer]

Well I can take care of moving netk out of libxfcegui4, not very
difficult to do. I'll also move some only-used-by-panel widgets into
the right plugin or add it to libxfce4panel (don't think the latter is
really needed).

Anyway, we first have to agree what we're going to do with gui4 and a
good name for the netk library (probably something like libxfce4netk)
before its API break time ;).

Nick