Completely cover `Couple` with tests

These are kind of silly, but 100% is 100%...
Use `Scrutineering.place_one_dance`

It simplifies things slightly and improves test coverage.
Replace deprecated `:finder_sql` with `Arel`

The poorly-named `prelim_results` association used the deprecated
`:finder_sql` option to `has_many` to get it to execute custom SQL.
Replacing this with Arel removes the deprecation warning and gives me
warm fuzzy feelings of modernity.
Quiet down RSpec and Coveralls console output.

They both spit out needless info, so quiet them down for less noisy test
runs.