Merge pull request #19 from NicolasKessler/master

conecting to web service and requesting JSON implemented
some Exceptions need to be handled better and the network request needs to
be moved to another thread!
Added Mensa object, menu object, created Model object to parse JSONObjects and create mensas with menus
Merge pull request #20 from theodortruffer/master

Added Mensa object, menu object, created Model object to parse JSONObjec...