Improve performance in Android web, particularly when joining polls

[mensch72]

Joining a poll on Android from the browser takes too long, sometimes gets stuck, and sometimes opens the poll page before all poll data was synced.

Also, the web app becomes slow when several polls are joined.

Ideas:

• reduce tallying frequency
• optimize tallying process
• make sure poll page is opened only after all poll data was replicated once (how to check?)
• don't sync all polls, only the one currently open? (but then how to notice when options have added to a poll? maybe sync only option data when poll page not open?)