Add ability to create unversioned data instance

[csweaver]

I want to be able to create un-versioned key-value data instance specifically, but digging into the code it looks like if you are going to allow it for one, you might as well add it to all types.

    POST /api/repo/{uuid}/instance

Creates a new instance of the given data type.  Expects configuration data in JSON
as the body of the POST.  Configuration data is a JSON object with each property
corresponding to a configuration keyword for the particular data type.  

JSON name/value pairs:

REQUIRED "typename"   Type name of the new instance,
REQUIRED "dataname"   Name of the new instance
-->OPTIONAL "versioned"  If "false" or "0", the data is unversioned and acts as if 
                      all UUIDs within a repo become the root repo UUID.  (True by default.)