Accounts, sessions and saves that follow you

Launcher pull request #149 reports each finished game run to Phaethon once, through an outbox on disk that survives being offline or signed out: the session's id, the game, its start and end, the seconds credited and the machine's name. On the account service, commit 7dc2969 keeps each report once per session id and sums the reports into play time per game, so a second PC's play adds up on the same account, and commit e14caca keeps each game's saves as revisions of one zip, the newest five per game, each written in full and flushed to disk before it is published under the account.