Change fk_glacier in table length_change.length_change_data from smallint to UUID

[yweidmann]

Currently, the table length_change.length_change_data uses the VAW-internal ID (stored as smallint, table base_data.glacier, column pk_vaw) as foreign key to the table base_data.glacier.

This foreign key should be replaced by the usually used column base_data.glacier.pk.

The data input files of VAW do work with the VAW-internal ID. The Python API for reading and inserting the data (project dataflow) already reads the base_data.glacier.pk.