add bin/mtest for running tests in multiple processes.
Update readme, describing bin/mtest.
Reactivate the wrongly disabled statefilter for dossier listings.

With the adjustments in the PR #426 the statefilter for dossier listings gets disabled by mistake.
This PR reactivate it.
Merge pull request #571 from 4teamwork/reactivate_dossier_statefilter

Reactivate the wrongly disabled statefilter for dossier listings.
Merge pull request #566 from 4teamwork/jone-threaded-testing

Parallel tests with bin/mtest
Referenceprefix manager: Made prefix-mappings of already delete objects removable.