Write utility to create reference image for motion correction

[danielsf]

Based on experimentation with Suite2P's reference image generation routine, we have found that Suite2P reference image generation can fail in the low SNR regime. Specifically, it fails by wrapping the field of view vertically or horizontally. This failure propagates to the motion corrected movie. It is our hope that creating a properly generated reference image will solve this problem.

Tasks

• [x] Generate small test input and output data from hacked Suite2P branch (@danielsf and @morrisoncb know what that means)
• [x] Add utility in ophys_etl_pipelines (that can depend on Suite2P) to generate a reference image

Validation

• [x] Test performance of utility against test data from hacked Suite2P branch. Make sure that we get bitwise identical results.

[morriscb]

Finished up the function after testing it against the test data provided by @danielsf. All data were found to produce identical results to the hacked version of suite2p, thus we are confident the code presented here is working as intended. Once this ticket is merged we can hook up the compute_reference function into the registration pipeline.