Survive server restart

[gbtami]

Heroku initiates daily server restart in random times. See https://devcenter.heroku.com/articles/dynos#restarting Stuff needs to be saved/restored are

• [x] correspondence games
• [x] lobby chat
• [x] seeks
• [x] games
• [x] tournaments

[mattgatto]

save-regular-seeks-across-restart.diff.txt

There's almost certainly a more elegant way to do it than adding the @property seek_json to seek.py, but, I haven't figured that out yet. It does work, and it fixes the bug gbtami mentioned on discord, where, if there's no correspondence seeks (because they got deleted in current server session), the last correspondence seeks from the database get restored, when the server restarts.

[mattgatto]

[gbtami]

Seems OK for me. PR please :)

[gbtami]

Thx!