Added generic signals between Core and GUI. You can use these to avoid having to...

signals for everything you need to send. This uses the usual mechanism, but instead of sending
custom-named signals and perform a parameter conversion, we just emit the raw data and leave
the processing to the user. Note that this might have a slight performance impact on the receiver's
side if you connect the generic signal to several custom slots, because _all_ unhandled signals
are sent to _all_ generic handlers (which then need to filter out whichever signal they need).

Use as follows:
- define signaltype in main/proxy_common.h
- use slots CoreProxy::csGeneric(type, arg1, arg2, arg3)
         or  GUIProcy::gsGeneric(type, arg1, arg2, arg3)
- On the other side, the signal is emitted by the proxy, so you may connect your slot
  and then handle the sigtype as needed.