Allow dictionaries to specify minimum compatible Yomitan version

[stephenmk]

On more than one occasion, I've had users report to me that they could not import Jitendex because they were using an older version of Yomitan.

If it were possible to specify a minimum Yomitan version in the dictionary's index.json metadata file, Yomitan could check the version and inform the user that they need to update Yomitan in order to use the dictionary.

[stephenmk]

Noting that this was probably the purpose of having different schema versions, but those haven't been incremented since the yomichan days.

[Kuuuube]

I think the schema versions are intended for breaking differences only. So if a change was made that broke backwards compatibility with older dicts.

Currently all dicts on the current schema version validate against the current schema just fine regardless of the age of the dict.

[stephenmk]

I also get people asking me why my dictionary doesn't work in Jidoujisho, so something like a "minimum version" field would have been good to have a long time ago. But it would be better late than never.

[stephenmk]

Implemented by #1750