low-level roach interface additions/changes

[laroque]

useful methods we'd like for roach testing:

• method that returns an array of time samples (flattens the internal 4 add channels to a 1-d array)
• method that returns the current ADC calibration values in some reasonable structure
• why are ArtooDaq methods being accessed not via self.?
• add phases to roach2_interface.calibrate_manually(...)
• add tone-based calibration method to roach2_interface

... not sure what else off the top of my head

[wcpettus]

• for 1 do you just want it returned to the command line? or will this get large enough it should get sent directly to file?
• for 3 we just need to mind the name conflict on set_gain being overwritten, but otherwise I think we should do that

[laroque]

This is becoming a mess of an issue, but I'll keep dumping things for now. It looks like the CFA has implemented calibration methods here: https://github.com/sma-wideband/adc_tests/blob/master/rww_tools.py (see set_freq, which tries to set the input frequency, and scans which call it).