Add BPMN for zensus data import and preprocessing

[gplssm]

fix #329

[IlkaCu]

The documentation seems to describe the script 'ego_pp-destatis_zensus_import.sql' correctly, but the input tables 'orig_destatis.zensus_population_per_ha' and orig_destatis.zensus_population_per_ha_grid' do not (anymore) exist in the database.

[gplssm]

Thanks for the hint!
Tables are initially uploaded into orig_destatis tables and the further processed and move elsewhere. I'll update the documentation when automized this section #339. It's quite likely this part will be replaced by some python 🐍

[gplssm]

One question come up during updating the BPMN. How to deal with tables that are temporarily used and droped after the end of the section? For example, for importing raw zensus data tmp_destatis.zensus_2011_pop_per_ha is created (plus 2 more tables) and 2 scripts later it's deleted again. By now, I didn't document/colorize the table differently

[IlkaCu]

As the tables name indicates its temporary use it should be okay to document it in the same way as the permanent tables.