EarthScope 2023 short cource update (insarlab#56)

+ create `workflows` folders for `smallbaselineApp*.ipynb` files and its auxliary files, for simplicity and independence

+ 2023 EarthScope update:
   - update course info: date/links, etc.
   - replace utils.ipynb with utils.py, to avoid the dependency of `ipynb` package
   - docs/requirements.txt: remove ipynb as it's not needed anymore due to the above change
   - add workflows/data/UCERF3_Fault.lonlat and plot faults on top of velocity maps
   - add move notebook related image files from docs/ to workflows/docs/
   - simplify the phase anatomy description
   - add temp coh and spatial coh question selection box
   - light re-arrangement of equations for closure phase bias.

+ README: update square badge style, to be consistent with mintpy

+ LICENSE: switch from GPLv3 to GPLv3+, to be consistent with mintpy

water_mask: add --fill while calling geocode.py (insarlab#47)

* water_mask: add --fill while calling geocode.py to better handle the no-data-value region, outside of the frame/burst/swath definition, e.g. in S1.

* smallbaselineApp_aria: use info.py --date --num --compact

plot_dis_ts: update usage to mintpy-1.3..1 (insarlab#35)

Update the usage of `mintpy.utils.read_timeseries_lalo()`, to be consistent with mintpy version 1.3.1.

update link to 2020 UNAVCO course on youtube

+ update link to the 2020 UNAVCO recording from google drive to youtube
+ update python version from 3.5+ to 3.6+ to be consistent with the mintpy repo.

update paper reference