Extract peaks

Adds functions to extract peaks from raw traces and save them as processed data (h5 xarray dataset), by default in usr/processed_runs folder. Adds function to load the processed data.

1. These functions can be used by damnit to process runs as they are created.
2. Currently, the loading of the processed data is done with the function load_processed_peaks(), but this could be integrated into the load function. However, it will require even more arguments to the load function which has already a lot.

Any suggestions @carinanc @lleguy @teichman ?