Disable docproperty updating in YearfolderStorer process.

The `YearFolderStorer` has to change security context (`AccessControl.SecurityManagement.SpecialUsers.system`) to move the forwarding and their containing documents to the yearfolder. Therefore we have to disable the DocProperty updating during the YearFolderStorer process, because the `SpecialUsers.system` does not have a userid etc.
Merge pull request #674 from 4teamwork/pg_yearfolderstorer_disable_docprops

Disable docproperty updating in YearfolderStorer process.