Add polite odk.py error response for non-parseable yaml.

[ddooley]

I was trying to get ODK to run the seed-via-docker.sh command to create an initial configuration (via "> sh seed-via-docker.sh -c -C foodon-odk.yaml") and didn't notice one line of my foodon-odk.yaml file was syntactically invalid. ODK errored out with the following cryptic message:

File "/tools/odk.py", line 829, in load_config
    project = from_dict(data_class=OntologyProject, data=obj)
                                                         ^^^
UnboundLocalError: cannot access local variable 'obj' where it is not associated with a value

I fixed the syntax error, and the above went away. Can ODK be revised to indicate politely when the input yaml file can't be parsed?