Add ordering to properties where required

[DanSmith]

This work is based on the requirements in #23

Ordering was added to:

• Item Groups
• Variables in records
• Group/Study/Datacollection structures
• Survey Instruments

[wlthomas]

VariablesInRecord was not originally intended to define order of variables. That was done in the physical description. A logical record could be organized in multiple ways. If this is optional, I guess its OK.

[wlthomas]

Why are these ordered? Just curious

[DanSmith]

I've reviewed the items listed in #49 for cardinality checks.

Several of the items on the list were actually 0..1 in the schema so no changes were needed.
Items that had a mismatch in cardinality between the 3.3 schema and the model were updated in d5212b8