Fix EZP-20867: Error when creating Image fieldtype without validator configuration

https://jira.ez.no/browse/EZP-20867

Similar approach used in: https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/Core/FieldType/TextLine/Type.php#L48
EZP-20866: create relations for new draft
Resolved todo: add contentclass-identifier to RelationList stored XML
EZP-20866: tested creating draft from Content with existing relations
Fixed EZP-20859 Twig exception trying to generate path to legacy module with no views
Merge pull request #361 from fdob/patch-1

Fix EZP-20867: Error when creating Image fieldtype without validator configuration
Merge pull request #362 from ezsystems/fix-EZP-20866-draft-relations

Fix EZP-20866: Creating Content draft does not copy relations for the new version
Fixed: Unit tests skipped because of unknown sequences

Partially reverts 933ad091aaadd1109ed60deb0dba77b07c917206
Changed: Uniformize fixture schema file to easily compare them

Fixing many schema differences while doing this.
Implemented EZP-20851: Setup Travis tests to also test prostgres for ezpublish-kernel & -legacy