Draws slope vs (synchrony, jitter) and saves to png

imshow colour plot
Bug fix: Argument order in firing_slope() caused unintended behaviour
Function spacing (PEP)
Skips function call if no spikes are present
Spacing
Code reformatting
Creating calibrate frequencies function
Formatting
Formatting fixes and import statements
Copied genInputGroups from DataGen

Might replace SynchronousInputGroup or should at least be merged. Both
are not required and I believe one is more efficient than the other.
Firing rate calibration working (not fully tested)

Appears to work but is extremely slow and stupid. Could use some
optimisation.