Add test that fails due issue #4
Delete the old value of the "WithoutID" relation if any

This fixes issue #4 and makes the related test pass.
Also renamed test.
More elegant solution for RelationType.fromString

make use of the rawValue initializer.
Merge branch 'feature/4-fix-withoutid-duplicate-import' into develop
Merge branch 'master' into develop
Renamed CDKWithoutID to CDKEmbedding

In line with relation names from http://microsoft.wikia.com/wiki/WinFS#Relationships

This is a partial fix for issue #5
Use CDKMapStrategy instead of CDKNoMapping value
Rename RelationType.RelatedById to Reference
Improved error messages about unsupported relations