Issue 2223 mapping name importer source

[PiispaH]

spine-tools/Spine-Database-API#423

Re spine-tools/Spine-Toolbox#2223

Checklist before merging

• Release notes in Toolbox repo have been updated
• Unit tests have been added/updated accordingly
• Code has been formatted by black
• Unit tests pass
• Change back to default requirements

[codecov]

Codecov Report

Attention: Patch coverage is 9.09091% with 10 lines in your changes missing coverage. Please review.

Project coverage is 62.33%. Comparing base (752e7c7) to head (64c91d3).

❗ Current head 64c91d3 differs from pull request most recent head a867b89

Please upload reports for the commit a867b89 to get more accurate results.

Files	Patch %	Lines
spine_items/importer/flattened_mappings.py	0.00%	4 Missing and 2 partials ⚠️
spine_items/importer/mvcmodels/mappings_model.py	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #214      +/-   ##
==========================================
- Coverage   62.36%   62.33%   -0.04%     
==========================================
  Files         168      168              
  Lines       17741    17750       +9     
  Branches     2951     2955       +4     
==========================================
- Hits        11065    11064       -1     
- Misses       6074     6080       +6     
- Partials      602      606       +4     

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