Create a shadow voting system

[flagbug]

This PR introduces a "shadow voting" system.
This means adding a song to the playlist as guest costs a vote, without actually voting on the song and thereby changing it's index in the playlist

Todo:

• Remove the playlist timeout, since we're moving to the new system
• Rename the voting system to "guest system"
• The guest system should only be able to be activated if there's a password set. Otherwise everyone has administrator rights anyway.
• Warn the user if there's a blank password set, since the administrator access won't work otherwise.
• Fix all the tests
• Reflect these changes in the mobile API
• Write five million more tests