0.8.2: stay signed in

Stay signed in.

• No more signing in again every day. GitHub's sign-in for this app expires after eight hours and comes with a refresh token that lasts six months; the app threw the refresh token away. It now renews the sign-in by itself shortly before it runs out (web, desktop, phone), and asks you to sign in only when GitHub refuses the refresh token.
• One sign-in per GitHub account on a device: every chat joined with that account uses it, so signing in again once mends all of them, and other open tabs pick it up.
• A lost connection, an outage or a rate limit no longer reads as being signed out; Settings offers Sign in again only when GitHub refused the account.
• Setting the password for a new account no longer fails with "Could not commit: the branch kept moving" (the browser served the branch from its one-minute cache). The CLI's commits benefit too.
• The password and chat steps have Back and Sign in with another account; a reload no longer keeps you stuck there.
• The desktop app and the phone sign in with scope sets of their own, so a web sign-in can't cost them theirs. The Android app keeps its sign-in out of backups and device transfers.

Chats signed in before 0.8.2 hold a token without a refresh token: sign in once more (Settings → Sign in again) when GitHub asks, and from then on the app keeps itself signed in.