VectorialTable working with models w/o foreignkey

Now the VectorialTableHandler can filter tables
using columns that are not explicitly set in the
model, as long as the field name exists in the layer.
It adds the column, filters by it and then removes it.
If the foreign key column is in the model, then the
column stays after filtering.
Primary key retrieval unified in forms.

Now all the forms retrieve the primary key from
the FormController in a similar way.
N:N relationship tables explicitly redrawn.

We have included a new method for redrawing the
N:N relationship tables, which has to be called
if we have an empty table.
NavTableForms lib updated.

It includes minor changes for preventing undesired
exceptions.