Add conversion for fiber photometry data from Elena He

[weiglszonja]

Fiber photometry from Elena He:

• ongoing data collection
• using abf format: Axon Binary Format
• channels = ['520sig', 'fxn_gen', 'opto_TTL', 'camera', 'treadmill']
• Add '520sig' is the fluorescence traces (voltage) for the green fiber AND 'treadmill' which is the velocity from the treadmill (voltage)
• The other channels 'fxn_gen' is probably the excitation source 470 and 405 similar to the other experiment, we have the TTL pulses for the optogenetic stimulus and the camera (adding in a follow-up PR as TTL sources)

[weiglszonja]

Example file:
#39 (comment)

[alessandratrapani]

LGTM!