added HDR gain control to thinkRF API, and device properties
added HDR gain controls to device controls panel
limited hdr gain control to -10 - 0
added gain/attenuation controls to amplitude group box
removed whitespace
created a amplitude controls class
fixed plots not being centered properly
removed print statements
fixed min level/ref level controls not showing
added if statement that was removed
fixed GUI hiding wrong widget
removed reference to playback box in device control
update attenuator box whenever playback is changed
Merge remote-tracking branch 'mfarhan/hdr_gain_control'

Conflicts:
	pyrf/gui/gui.py
	pyrf/gui/trace_controls.py