Improve config file handling: Default settings, changed settings, etc.

[nattthebear]

Config.ini breaks and everyone cries.

Default settings change and users with existing config.ini files don't pick them up.

What can we do? I don't know, it's a big problem because there are a lot of assumptions baked into our config system.

TODO.

[YoshiRulz]

The possibility of a config importer has been available since 8bb9cee. I'm imagining a clever use of wrappers and inheritance to make the deserialiser do all the work instead of checking each version/property.

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@TiKevin83 suggested in IRC that if a movie is loaded and its SyncSettings schema doesn't match the current version of the core, the user should be asked to pick the equivalents of the old values (or the core could provide SyncSettings importers, but that probably won't happen).

[nattthebear]

SyncSettings schema

I don't think we're tracking this at all right now, so it's not something we could do retroactively.

[YoshiRulz]

Does our JSON library not support something like that? I would have thought comparing the key names would be enough to determine if it had changed.

[nattthebear]

As I explained in IRC, if a property is missing in the old settings but present in the current schema, we do not know for sure why it's missing; whether it be from a different schema, or just the value wasn't present.

Also, real talk: While generally improved config handling is neato, is this particular SyncSettings fixup valuable beyond fixing a handful of gameboy movies?