core.py

- Remove minStartTime, maxStartTime and outdir as default arguments
- Adds notes ot documentation on which arguments are optional
- Change log-level on some command line calls that dont' matter
- Reorganise the tests performed after loading the data
- If minStartTime and maxStartTime are None, set them using
  SFT_timestamps
- Remove default labels from plot_twoF_cumulative
- If add_pfs is called, call generate_loudest automatically
- Save min/maxStartTime in pickle and load if required