Load GudPy work from project folder

[rhinoella]

Allows GudPy to be loaded from a previously outputted project folder. Supports the move from input files to project folders in #457.

• GudPy still supports loading from input files
• When an input file is loaded, when the user sets a save location, a project folder is created there and a new copy of the input file will exist there (GudPy will not overwrite existing input files outside of a project folder)

[github-actions]

Test Results

  3 files    3 suites   1h 1m 22s ⏱️
 93 tests  93 ✅ 0 💤 0 ❌
279 runs  279 ✅ 0 💤 0 ❌

Results for commit 506ddc8.

♻️ This comment has been updated with latest results.

[trisyoungs]

Looking through this really made me appreciate what a nice idea this was in the first place. I fully believe this is how it should be.

Few minor comments (questions, really, for my own benefit!) to address before merging, but otherwise looks good.