Add a generic object for unit tests

Summary:
A later diff adds unit tests against edges, but we need real objects to connect with edges. Add some trivial objects to the Harbormaster database to compliment the similar HarbormasterScratchTable.
On its own, this does nothing interesting.

Test Plan: Built unit tests on this in a followup.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1162

Differential Revision: https://secure.phabricator.com/D2937