Dropped no longer used contact_information utility query.
AdminUnit builder: assign org_unit to admin unit when wrapping a orgunit.
Fixed AdminUnitBuilder: dropped doubled `after_create` method.
Introduce a specific query class for the Task sql-representation.

The query class should replace the ITaskQuery utility in the feature.
PersonalOverview: Rework tasklistings, so that all view queries the Globalindex.
GlobalIndex Syncer: convert sequence_number to a str for the sql-representation.

Right now the Sequencenumber is a String field in the task model,
therefore we have to be sure that the `sequence_number` and the
`dossier_sequence_number` are converted to a string.

The DB model should be ajusted and migrated in the feature.
Merge pull request #283 from 4teamwork/pg_task_tabs_rework

Rework personaloverview tasklistings
Migrate data for issuing_org_unit.

Issuing org-unit is always taken from the first
task in a task-chain.