Refactoring and testing complete. (+13 squashed commits)

[vickdw]

Squashed commits:
[abeb938] Should have all Symbol Sets correctly coded and User experience with the drop downs fully coded and bug free. (fingers crossed.)
[b5b472d] more refactoring
[0a7e0ac] more refactoring
[fde6ed3] more refactoring
[6c8dcf9] more refactoring
[a4ddae0] more refactoring
[8e059cd] more refactoring
[4b27b14] continuing edits to LandUnitSymbolSet
[ec937bc] continuing edits to LandUnitSymbolSet
[11afe22] building out the land unit symbol set.
[7ac134b] building out the land unit symbol set.
[3d788a1] refactoring, creating individual classes for the respective symbol sets. Have updated UI to reflect the workflow of
https://explorer.milsymb.net/#/explore/.
[4a85413] Make SIDC dialog run-able; use old-style ui import for code completion

[dakcarto]

Initial testing...

• The SymbolSets.py file should follow Pythonic naming, e.g. symbolsets.py. The file is missing a copyright header. Each class in the file should inherit from a base class, maybe SymbolSet, instead of reassigning all of the instance variables in __init__(), which I don't think is doing anything now.

• When testing, I noticed the renderer showed correct symbol, but not the edit dialog (Entity is not set to 11 Military for code 10010535221100000000):
  

• Then, after setting Entity to 11 Military, and then trying to set it back to 00 Not Applicable, this error is thrown:
  

• The edit dialog has been changed, so the Windows screen snap in the docs need updated, as well as any associated text.

• Please update the copyright headers for files you have worked on, e.g. add this year, etc.

• Most importantly, there are no unit tests for the changes. While previously, the tester plugin was used functionally, I think there needs to be a suite of regular tests that cover many comparisons against control images. Ideally, the dialog itself could have UI tests run using QTest, which can modify comboboxes, etc, then a test of the generated image could be compared to control images.

  To accomplish this, I should probably set up the tricky test suite, then one can continue to add more comparison tests.

[dakcarto]

Best not to issue print() commands from a plugin, except for when debugging inside of QGIS, which I'm guessing this is for.