Arduino: first cut at impedance detection
ProcessingGUI: click on FFT plot to get the value
Arduino: impedance, no lead_off on P inputs
Merge branch 'Adding-Impedance-Checking'
Arduino: can turn Lead_off for P and N independently
Processing GUI (full): better handling of key presses
OpenBCI_GUI: abstracted the start/stop behavior a bit.
ADS1299Manager: improve init, bias, LOFF_FLIP

Improve initialization sequence and added initialization of of the
LEAD_OFF parameters.  Added LEAD_OFF FLIP to swap the polarity of the
injected LEAD_OFF signal based on V1 vs V2.  Finally, for V2, we now
generate the bias based on both the N and P inputs, per Joel's
suggestion.
OpenBCI_GUI: full control over LEAD_OFF functions
Processing_GUI: shows railed signals on head plot
OpenBCI_GUI: add button to reveal Lead_Off buttons
ProcessingGUI: added data labels and plot titles
ProcessingGUI: turn off synthetic data
ProcessingGUI: fixed "railed" alert, format of chan values
ProcessingGUI: refactored color calc in headPlot
ProcessingGUI: first cut at shading the head based on electrodes
ProcessingGUI: shading of head fully working
ProcessingGUI: quantized the colors to make contours
ProcessingGUI: clarified the ADS1299 scale factor
ProcessingGUI: can now turn off the contour head plot