Rewrite TitleHelper stuff: split it up

... into 2 pieces:

#1: PropertyHelper which provides basic functionality
    to handle certain properties (e.g. rdfs:label) and
    to query the database.

#2: TitleHelper as the first extended class of the
    PropertyHelper. It will specify the properties and
    other functions for the certain use case of querying
    titles/labels from the store.