Implement peer-to-peer

[tillsanders]

Allow users to generate links that can be shared with friends for combinated results.

[tillsanders]

Todos from alpha phase:

• [ ] Improve modals on mobile, especially in combination with the main navigation
• [ ] Make input of peer id uppercase
• [ ] Add notifications for guests "knocking" (host), joining (other guests) or being admitted (joining guest), with quick action
• [ ] Lost connections are not revived automatically. Maybe own peer id and recent host peer id should be saved to LocalStorage.
• [ ] Buttons in main navigation should be disabled when participating in a shared session.
• [ ] Add some form of "advertisement". Maybe a button somewhere on the start page?
• [ ] Generate links for easier sharing

More advanced ideas (for later):

• [ ] Show how many friends have completed the compass at the start of the comparison section
• [ ] Show statistics: what parties got the most points, what parties where selected the most, which theses are most controversial, what theses was skipped the most
• [ ] Integrate with analytics