Support adding credentials for basins on S3

[paulmueller]

My laptop is broken so I am pushing this to a new branch so I can work with a temporary device.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.38%. Comparing base (f021a48) to head (d2b8ce0).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
shapeout2/gui/main.py	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #179      +/-   ##
==========================================
- Coverage   79.39%   79.38%   -0.02%     
==========================================
  Files          64       64              
  Lines        7062     7071       +9     
==========================================
+ Hits         5607     5613       +6     
- Misses       1455     1458       +3     

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