progress on multiple api server support

[domino14]

Support multiple API servers. This is important during deploy.

• Invalidate game cache if turn sequence numbers don't match. Reloading game from db, even one that is almost done, only takes on the order of 1 millisecond
• Add a soughtgame db store so we don't lose seeks during deploys

[domino14]

this is going to be handled differently, as in #889

see #905 eventually