Yell Budgeting Tool: Database Primary Key conflicts

Due to the synchronizer currently re-generating the hierarchy with each run, the
internally-generated primary keys for the Yell tables will keep increasing, and
at some point reach a maximum value. Simply resetting the keys will not fix
this, as existing rows will cause duplicate exceptions.

The correct fix is to change the synchronizer to not delete/re-generate rows,
but only create new BT/BF/TL objects if necessary. The mapping table used to
map parents/child relationships can still be cleared; it is completely wiped,
and thus resetting the primary key index value to one will not have an adverse
effect.