fixing LIS groundwater trend analysis and comparison to GRACE

[aaarendt]

• this PR fixes a few small bugs in the original notebook and cleans up the code
• a few refinements are also made to the himatpy package to simplify and standardize data ingest

[pep8speaks]

Hello @aaarendt! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file himatpy/GRACE_MASCON/pygrace.py:

Line 251:80: E501 line too long (100 > 79 characters)

• In the file himatpy/LIS/utils.py:

Line 17:80: E501 line too long (115 > 79 characters) Line 26:53: W291 trailing whitespace Line 47:80: E501 line too long (100 > 79 characters) Line 49:1: W293 blank line contains whitespace Line 55:9: E722 do not use bare 'except' Line 56:80: E501 line too long (92 > 79 characters) Line 58:1: W293 blank line contains whitespace Line 72:80: E501 line too long (82 > 79 characters) Line 73:10: W291 trailing whitespace Line 77:80: E501 line too long (99 > 79 characters) Line 78:27: E231 missing whitespace after ':' Line 78:49: E231 missing whitespace after ':' Line 78:65: E251 unexpected spaces around keyword / parameter equals Line 78:67: E251 unexpected spaces around keyword / parameter equals