Fixed MigrateAdminUnitOrgUnitSchema upgradestep, get foreign key constraints names dynamically.

(cherry picked from commit 47a16b90d5195212fa490571737ddd59e09bd62c)
Fixed MigrateAdminUnitOrgUnitSchema upgradestep: dropped unnecessary column change.

(cherry picked from commit cde9633e34cefafcf7bc994faa6540acf2c04c04)
Fixed IncreaseColumnLength upgradestep, get foreign key constraints names dynamically.

(cherry picked from commit d4030923b52cd66962f859f5f9f00ee84f57b1a9)
Fixes IncreaseColumnLength upgradestep for oracle, removed wrong `nullable` parameter.

(cherry picked from commit c2721b3f3b5db58bf66cd1cfc79d2c9904a8f1cd)
Dropped not necessary `new_column` attribute in IncreaseColumnLength upgradestep.

(cherry picked from commit 7d68ee60392c5caeec1ad0153af7a509baefcb9f)
Fixed MigrateTaskTable upgradestep.

Migrate data before making the `issuing_orgunit` column required,
because the oracle DB is more strict in this case.

(cherry picked from commit cf0b3142cfe11f30538fec0c4022a93e546a974e)
Disable temporarily removing unique constraints when using Oracle as OGDS DB.

Because oracle can handle column renames with unique constraints.

(cherry picked from commit 7fefa1bd94a8629abfbc95524a30a0f29064ec42)
Fixed DB connection setup in the SchemaMigration class.

This allows transaction rollbacks when the upgrade fails.

(cherry picked from commit c8828068372da533a3551947f39374cc0ccbbd12)
Made AlterSequenceNumberType upgradestep oracle conform.

Because oracle does not support changing column type's from String to Integer,
we had to implement an oracle specific way with an temporary column.

(cherry picked from commit ccc6f3156506dad8ea721f28bafb5b721b553b1d)

Conflicts:
	docs/HISTORY.txt
Fixed transporting task with the OGDS Transporter between different admin_units.

The commits 9b75a9d and 910c829 brakes transporting tasks with the
`opengever.ogds.base.transporter.Transporter` from one admin unit to another.

I've added an tests for transporting tasks and refactored the `Transporter` object creation completely.

(cherry picked from commit 140e9ee9e4532dffc8c23fb644e7d79c7bbc15cb)

Conflicts:
	docs/HISTORY.txt
Dropped no longer used interface `ogds.base.interfaces.IObjectCreator`.

(cherry picked from commit a353c0b14ed707a240e1ad91f3a673a6d312ce88)
Dropped the ITransporter utility and replace it with a simple object.

(cherry picked from commit 2703bb54d4cf7d8897c59c644493c4a87c91b04b)
Merge pull request #695 from 4teamwork/pg_4.0.6

Prepare bugfix release 4.0.6.