Relational Save Data / ORM Manager

[The-Fireplace]

Is your feature request related to a problem? Please describe.
As a mod developer, it is limiting and inefficient to use the current JSON-backed save data helpers. Although it would help to allow substituting in some other backend storage, ultimately it still has limitations, such as the single primary key restriction.

Describe the solution you'd like
New Relational Save Data manager which allows for:

• Multiple column primary key
• Indexed non-primary columns
• Querying by specific columns (equals, not equals, greater than, less than, AND/OR with other conditions)

Additional context
This could mostly use the storage buffers that were already designed, but I'd have to remove the list/map support again since we'll be using a proper database structure. The current system of reading from and writing to buffers seems to be a good way to abstract out for the new setup.