Update DocProperties for Documents that already have them.

Update DocProperties for Documents that were created with DocProperties (either from a gever document template or by uploading a new file with DocProperties) when:
- moving/copying documents
- after checkout/checkin

Furthermore, create a journal entry when updating DocProperties

Closes #509 
@lukasgraf hm, good point, me neither :expressionless:. I removed the classmethods and some duplicated checks.