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.
Fixed EZP-20899: FieldDefinition appears unsorted while they should be ordered by placement
Implemented EZP-20851: Setup Travis tests to also test prostgres for ezpublish-kernel & -legacy
Merge pull request #364 from patrickallaert/EZP-20851

Fixed EZP-20899: FieldDefinition appears unsorted while they should be ordered by placement + Implemented EZP-20851: Setup Travis tests to also test prostgres for ezpublish-kernel & -legacy