pseudo-merge from pyrf/master
Merge remote-tracking branch 'pyrf/master' into waterfall

Conflicts:
	examples/waterfall_crosshair_demo.py
	pyrf/gui/waterfall_widget.py
added waterfall.set_lookup_levels and connected to rtsa-gui plot controls
tidied the last commit
Merge remote-tracking branch 'pyrf/master' into waterfall
Merge remote-tracking branch 'rwarren/waterfall'