GEOPY-2003: Add UIJson class for gravity forward/inversion

[benk-mira]

GEOPY-2003 - Add UIJson class for gravity forward/inversion
Patch for default_ui_json paths

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.60%. Comparing base (11fa7d3) to head (9a63e57).
Report is 71 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #166      +/-   ##
===========================================
+ Coverage    88.95%   89.60%   +0.64%     
===========================================
  Files           77       81       +4     
  Lines         3940     4597     +657     
  Branches       547      606      +59     
===========================================
+ Hits          3505     4119     +614     
- Misses         302      323      +21     
- Partials       133      155      +22     

Files with missing lines	Coverage Δ
simpeg_drivers/potential_fields/gravity/uijson.py	100.00% <100.00%> (ø)

... and 8 files with indirect coverage changes

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