Small bug fixes for meal dao and service

Service did not callback proper listener method (called onNextWeek()
instead of onCurrentWeek).
Content dao did not create current/next week days properly. It also used
them in an incorrect way inside the sql query (missed sql date()
function and used wrong formatting of dates in general).
Adds german toString() implementation for menu and meal entities
Adds rough implementations for cafeterias, menus and meals ui