[TASK] Convert the RSpec tests to the new "expect" syntax.

RSpec's old "should" syntax creates a bunch of problems. This change converts
all tests to use the new "expect" syntax and disables the "should" syntax in
the configuration.
[CLEANUP] Refactor the tests.

This change refactors the tests as recommended by the Rails Style Guide.

- drop the unused user from the factory
- add a test for a generally valid model
- use the valid model as basis for the model tests
- group the model tests by attribute
- rename the tests
Merge pull request #18 from braingourmets/cleanup/refactor-tests

[CLEANUP] Clean up and refactor the tests.