Make compatible with v2.0 hardware
Changes to i2c functions

* Add functions for getting/setting waveform voltage/frequency from
  signal generator board over i2c
Add config values for switching and signal board i2c addresses
Add send_i2c_command function
Add i2c_scan function
Fix A0 series resistors for v2.0
Rename send_i2c_command to i2c_send_command
Fix i2c_read commands
Fix set_waveform_voltage (v2.0 hardware) to account for amplifier_gain
Update edit configuration settings for v2.0
Fix calibration of hv attenuators for v2.0
Fixes #26
Fixes #27
Fix feedback related equations for v2.0