DOCS: Update CLI tutorial and add scripting tutorial. Use cached data.

[baagaard-usgs]

Documentation updates

• Update gmrecords command line interface tutorial.
  • Use data cached in tests/data/tutorials.
  • Run commands and capture output (previously commands were not run).
• Add tutorial on how to script GMrecordsApp to chain together commands.
• Update makedocs.sh script so that it keeps the _build/html directory; cache results so we don't have to run the notebooks every time we want to update the documentation. This make it much quicker to update the generated documentation and verify fixes.

Code fixes

• Fix title in regression (PGA versus distance) plot. Should be PGA vs distance and not distance vs PGA.
• Fix location of logging statement in compute_station_methods.py to avoid repetitive output.

@emthompson-usgs I added a comment in the process_waveforms.py about moving a logging statement outside a loop. Right now, we get repetitive logging statements. This should be updated when the parallel processing gets fixed.