Fix issues related to Rhythm API. Closes #147
Remove redundant updateRegister() call
Update to Rhythm API v1.4
Update RHD2000Thread for Rhytym API 1.4
Allow polarity of LFP to be inverted in the LFP Display
Allow spikes to be inverted in the Spike Display
Fix inversion logic of Spike Display
Allow SpikeDisplayCanvas to save and load parameters
Add repaint() call after inverting spikes