in set_content_units, support units without geography

[RobLBaker]

1. The units service will almost always be behind the lands division, which is also never going to be up-to-date. Some valid units in the units geography service will not have geography associated with them.

2. Invalid units and units without geography return the same result from the units API service for geography

3. This will require a 3-step process:
   a) An initial API call to verify whether a unit is valid or not
   b) A secondary API call to get geography, if it exists
   c) Adding the content unit - with or without geography - to EML

4. It will be important to verify that DataStore can handle content units without geography in metadata:
   a) When some content units have geography and some do not
   b) When none of the content units have geography
   c) When all of the content units have geography