Update requirements for Python version

[lbianchi-lbl]

Summary/Motivation:

• Update supported Python versions to 3.7 through 3.9
• Remove version constraint for pywin32 since it shouldn't be needed anymore
  • EDIT: it seems that removing the constraint results in errors, and therefore we have to keep the pywin32 version pinned to the older 225

Changes proposed in this PR:

• Remove Python 3.6 and add 3.9 to CI checks
• Update setup.py with Python version requirements and updates

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 30.76%. Comparing base (a3fcb81) to head (d4bd429).
Report is 108 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1014   +/-   ##
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  Coverage   30.76%   30.76%           
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  Files         161      161           
  Lines       35793    35793           
  Branches     6041     6041           
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  Hits        11013    11013           
  Misses      23966    23966           
  Partials      814      814           

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[ksbeattie]

LGTM

[dangunter]

@lbianchi-lbl I just ran into the Python 3.9+ not supported issue (since 3.10.x is default now), so I would suggest prioritizing a simple update to the install docs.

[dangunter]

Also a note on Windows in order to get the Foqus install (at least desktop shortcut) to actually work, I had to follow one of the more evil hacks suggested on this page https://stackoverflow.com/questions/58612306/how-to-fix-importerror-dll-load-failed-while-importing-win32api , namely copying the files pywintypes38.dll and pythoncom38.dll from the Conda environment Lib into my Windows system32 lib (!!!)

[lbianchi-lbl]

Closing this in favor of #1036 (for the Python 3.9+ support) and #1037 (for the issues with creating a desktop shortcut on Windows).