* Moved campvis::Runnable interface to tgt namespace (since it's needed by sigslot, which only depends on tgt)
* Introduced sigslot::signal_manager singleton class that will manage the dispatching of signals in its own thread
* Started proof-of-concept implementation of asynchroneous signals for signal0<> and signal1<>. Both classes define their own signal_handleN deriving from _signal_handle_base, which defines the signal to dispatch.

Proof-of-concept implementation seems to work so far.

refs #384

Conflicts:
	core/tools/opengljobprocessor.h
	ext/tgt/runnable.h

Conflicts:
	application/CMakeLists.txt
	core/tools/opengljobprocessor.h