Adding persistence verification for Thing

I want to make sure that the properties data stream is as expected. In
this particular case, since we are using a very rudimentary, and
ultimately meaningless schema, the verification is rather simplistic.

It does, however, highlight a proof of concept for verification.

@TODO - Extract the verify_persistence method into a custom matcher;
    Highlighting how to create a custom matcher is also a good exercise,
    as a custom matcher can provide greater clarity regarding what is
    begin tested.