Fixed bug in resp regressors, changed file format

There was a bug in the regressor calculation that affected the respitory
regressors. The extra data collected before the scan starts was not
properly clipped before running the regressor calculation. This is
fixed, and the regressors do indeed perform better. I also changed the
regressor.csv file format to a simpler style that can be more easily
read by programs that read csv files. Also added a method to write out
the raw data in json format. Both file writing methods now also allow
in-place gzipped output files by adding .gz the filname parameter.
Script to recompute physio regressors for all data