feat!: support multiple namespaces for the game

[imLinguin]

This is a breaking change that allows games to contain more than one asset per platform - meaning multiple sandboxes aka namespaces.

This involves breaking changes to how metadata.json is stored, as well as additional fields to installed game classes.
Sidecar configs were also separated into per-namespace maps.

Changes to metadata mean older versions of legendary will probably fail to read those files. I can try to make this as much backwards compatible as possible if desired.

Additional remarks:

• info and install commands support --namespace arguments now
• info output was slightly changed to incorporate multiple assets per platform
  • latest_version and manifest keys correspond to desired --namespace, by default its first public asset found
  • namespaces key is an array of available namespaces, their details and times when given license was obtained by user
  • platform_versions is now a {platform: [...assets]} object, instead of just versions

[CommandMC]

Changes to metadata mean older versions of legendary will probably fail to read those files. I can try to make this as much backwards compatible as possible if desired.

I'd say do this, yes