Made Institution, City and POI Models again

The previous changes didn't work as intended. Will look into it later if
I'll have enough time.
Removed the 'Settings' menu item
Created the FoodFragment and connected it with MainActivity

The fragment will be made of a list of a list and preferably of a
SearchWidget to filter the list. The SearchWidget doesn't work for now
because of unknown reasons. In another project it worked flawlessly with
the same configuration...
Fixed database relations

Fixed relations between Coordinates and Institutions/PointOfInterests.
Removed summary member with address member
Added WorkingHours class

The WorkingHours class stores a POI's working hours. One POI can have
multiple WorkingHours for multiple services it provides. WorkingHours
therefore also stores a summary of the service that's provided by the
POI.
Created PointOfInterestAdapter

Created an adapter to display points of interest on a ListView. A basic
layout is created as well and the FoodFragment was updated to load POIs
related to food.
Pre-populated the database with one POI with WorkingHours

Also fixed the data loading
Created the fragments for culture and 'other' POIs

They are pretty much just copy-paste but that won't be a problem I
guess.