Decouple UI tests from fixtures by using SQL dump of OmniFixture #349

Modified SetupFixture command so an SQL dump can be created for a fixture (& added docs). Used the command to create an SQL dump of OmniFixture that is used by UITestFixture to setup the database.

This change will allow changes in Fixtures to be made w/o having to alter expected screenshots in UI tests.

To create a new OmniFixture SQL dump, run the following commands:

./console tests:setup-fixture OmniFixture --sqldump=tests/resources/OmniFixture-dump.sql
gzip tests/resources/OmniFixture-dump.sql

This pull request will break UI tests.