Add versioning of local scores

[peppy]

For any potential future usage

Minimal implementation as to not spend too much time, just want to get this in place in case we need it.

[bdach]

I guess probably the only question I'd have here is - do we wanna put this in replays too (and decode it from there on import)? We can probably put this in LegacyReplaySoloScoreInfo with practically zero effort.

[peppy]

Oh yeah. I didn't realise this was so low effort, if so then let's do it.

[bdach]

Have done so in 2baf579 (with test coverage in 5ff95db).

[bdach]

As discussed on stream I've also renamed the property to ClientVersion in 81bbdcc because I feel we will have too many versions of everything otherwise and invariably get confused.

@peppy would appreciate double-check of changes. Importantly, if you're going to run this, remove client_40.realm* from the development directory, or else it will probably yell that the db is corrupt. This is because I did the rename without bumping schema version again.