Remove all code related to participating an event as an anonymous user

The code is currently unused. There are some notes about re-integrating
this feature, but I think in this case we should rebuild it. The code is
pretty unwieldy.
Typo Kalendar -> Kalender
typo
Merge pull request #496 from muescha/patch-3

typo: dieses ->  diese -> dieser
Merge pull request #492 from muescha/patch-1

Typo Kalendar -> Kalender
Merge pull request #463 from hacken-in/remove-attending-as-anonymous-user

Remove all code related to participating an event as an anonymous user
Merge branch 'master' into release