Update tests to remove deprecated use of ODM2 module hierarchy

[emiliom]

Doing this would make the output of the tests (eg, "warnings summary" on TravisCI, such as this one) much less cluttered and easier to digest.

Plus, we have to move away from that deprecated module hierarchy anyway. Better sooner than later.

Example of current warning output:

/tmp/tests/test_SessionFactory.py:3: FutureWarning: 
The module odm2api.ODM2.models will be deprecated. 
Please use odm2api.models instead.
 from odm2api.ODM2.models import CVElevationDatum, setSchema

[emiliom]

PR #170 started to address this. More changes are needed

[emiliom]

Completed by PR #171