Add buecher.sql; Change behaviour of ListModel

The data of a ListModel instance will not be saved in a list of integers, but
in an associative array of associative arrays of booleans, which means that it
is now possible for a form to have more than 31 books (limit of int).
Furthermore this way is less vulnerable and the view BTausch can now be dropped.
Added jump functionality to ListView

When pressing a key in ListView, the program will attempt to jump to the
name beginning with the pressed key, e.g. pressing 'b' will select the first
row containing a name that begins with 'B'. Moreover, the horizontal header
of ListView will now be 200 instead of 150 pixels high.