CSV-driven variable exports

[dangunter]

Fixes/Resolves:

(replace this with the issue # fixed or resolved, if no issue exists then a brief statement of what this PR does)

Summary/Motivation:

Allow variable exports to be listed in a CSV file instead of (or in addition to) Python API calls.
This is a more compact way to export a lot of variables.
Does not alter or invalidate the existing Python API export method.

Changes proposed in this PR:

• Changes in watertap.ui.fsapi
  • FlowsheetExports: new methods from_csv() and to_csv()
• Changes in docs
  • Added the from_csv() to the how-to on the API. Streamlined the page too.
• Changes in configuration
  • in setup.py, added importlib-resources for Python < 3.11 support for the features that "find" the CSV datafiles in the package directory

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (17d9679) 94.27% compared to head (30633b5) 94.27%.

Files	Patch %	Lines
watertap/ui/fsapi.py	91.48%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1232      +/-   ##
==========================================
- Coverage   94.27%   94.27%   -0.01%     
==========================================
  Files         357      357              
  Lines       35918    36011      +93     
==========================================
+ Hits        33863    33950      +87     
- Misses       2055     2061       +6     

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[bknueven]

One method is completely uncovered.