Write game category in database

[jgdhs27]

Game category (PC-98, Windows, and possibly more in the future) is currently hardcoded, but it could be in the database instead.

[32th-System]

You mean a database level constant (like what we do with shottypes and routes) so it can be used as a foreign key?

[n-rook]

I'm not sure if it should be a table or not. Unlike game or shot, the relationships involved are a bit less complicated, and it's not like we are likely to change it around much later. So I think it would be fine just as a data column in the game table.