Add retry handler for matrix rate limits

[aofn]

Uses retry_after_ms from the error response to await ratelimiting and retry the failed request.

• fix bug where creating rooms loops and doesn't proceed with adding the room to its parent
• display user feedback while syncing
• add translations
• use retry handler when creating application folder
• use retry handler when creating service folders
• use retry handler for /etherpad
• use retry handler for /spacedeck

Testing:

• try to encounter rate limits. for example create at least 8 sketches directly in spacedeck (not from within spaces! the more the better, since this should trigger ratelimiting by [matrix])
• open /spaces and go to /spacedeck
• /spacedeck will now try to sync all sketches and, if it runs into ratelimits, should automatically wait until it tries again

This PR continues from #71 after some technical difficulties 🧑‍🔧