Project can't use std.set and other DataTables simultaneously

[sraboy]

It's probably going to be kludgy code to maintain the backwards compatibility with 7KAA code but a user should be able to open multiple files, including those with their own data. See issues #11 and #12.

This is really only an issue when trying to save changes. The non-standard tables (not in std.set) should still be added to the ActiveGameSet but Project will need to iterate through the tables and pick out the (hardcoded) names of the standard game set and only save/return the appropriate ones (whether saving a ResIdx, dBaseIII or std.set).

[sraboy]

This had to wait until all the hack-ish stuff was removed because all the UI stuff was too tightly integrated with SkaaGameDataLib. Now, with an MVP(ish) implementation, it's much easier to account for. For the relevant commits that re-added GameSet saving, ResIdxMultiBmp loading and some changes to the dBaseIII "engine", see:
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