Fixes issues with ArrayValue

Addresses:
* Issue with list assignment of ArrayValue
* Issue with returning ArrayType values by improving handling of
O8 data

Adds 'interop' test in test_parameter_values to ensure returns are the
same with in-memory or persisted
Fixes issue in CategoryType when setting with None
Merge pull request #56 from blazetopher/pval_fixes

ParameterValue Fixes