Updates to case, observation, and submission

[erikogabrielsson]

Resolves issus #35 #17

Added

• BP.submission.xsd derived from SRA.submision.xsd with added BP types.

Changed

• CaseType is now included in SAMPLE_SET
• SpecimenType can optionally reference a case with the PART_OF_CASE-element, replacing the RELATED_SPECIMENS-element on CaseType.
• For ObservationType the item an observation is made on is moved to the OBSERVED_ON-element.
• Replaced StatementCodedAttributeSetType and StatementCustomAttributeSetType with common types BPCodedAttributesType and BPAttributesType.