RingtoetsProjectTestHelperTest.cs

Merge branch '1579'
# Conflicts:
# Application/Ringtoets/src/Application.Ringtoets.Migration.Core/EmbeddedResources/DatabaseStructure18.1.sql
# Application/Ringtoets/src/Application.Ringtoets.Migration.Core/EmbeddedResources/Migration_17.3_18.1.sql
# Application/Ringtoets/src/Application.Ringtoets.Storage/DbContext/RingtoetsEntities.edmx.diagram
# Application/Ringtoets/src/Application.Ringtoets.Storage/Ringtoets.rtd
# Application/Ringtoets/test/Application.Ringtoets.Migration.Core.Test/test-data/FullTestProject181.rtd
# Application/Ringtoets/test/Application.Ringtoets.Storage.Test/IntegrationTests/MigrationTo181IntegrationTest.cs
# build/DatabaseStructure.sql
# design/DatabaseDesign.eap