prohibit bannef user from creating event
add new API to ban user
add a button to ban on user page
fix broken test case
refs #485: replace URL length with 23
refs #485: replace literal with constant value
refs #486: disable cache to get correct data
Merge pull request #487 from eller86/485-too-long-url

FIx: too long url
Merge pull request #486 from eller86/ban-account

Ban account
Fix cancelled participations message.
Merge pull request #488 from mazgi/fix/cancelled_participations_message

キャンセルした人がいない場合のサイドバーメッセージを修正