mc-9808 Allow a simplified creation for ReferenceTypes and ModelDataTypes

[olliefreeman]

• Allow POST to DataTypes without a label for RTs and MDTs
• Generate a default label of "Reference to X" where X is the label of the reference
• Confirm the existence of the reference
• If a DT already exists with that default label then generate a new one with the next number in order suffixed
• Allow POST to DataElements without a label in the DataType for creating new DTs alongside the DE
• Use the default label for RTs and MDTs when creating a DE if no label supplied
• Try and find existing DT with same domaintype and label when creating a DE and DT at the same time.
  If the DT exists then use that one rather than creating a new one which will fail as the DT already exists

[olliefreeman]

test failures are to do with timings, not the code. need to increase the timeout for lock.