Migrate tests to use DBIx::Class::EasyFixture

[preaction]

Having raw data directly in the test case is ugly and makes it harder to read. Instead, move the test fixtures into a class in t/lib that uses DBIx::Class::EasyFixture. Each table should have its own fixture, and proper dependencies should be set up using the next feature (so, the release_summary table requires data in the release_data table which requires data in the uploads and cpanstats tables).

This will make it easier to read and write tests.