Separate valid GEDCOM 5.5.1 from invalid GEDCOM 5.5.1 into separate test files

[dthaler]

Currently date-all.ged and date-dual.ged contain both valid and invalid GEDCOM 5.5.1.
I would request that they be separated so that the valid ones can be used for validation/compliance/etc tests that would apply to most programs since the tests would implement recommended practices such as in the migration guide,
whereas the behavior of handling invalid GEDCOM 5.5.1 can legitimately vary by implementation and so other implementations would not be expected to match the GEDCOM 7 output.