Load the data for integration tests upfront

We can do it, because we use :transaction strategy with DatabaseCleaner,
which starts transaction before each test and rollbacks after it. That
way data before each test is consistent.

The big advantage of such approach is that tests are fast now - we need
to only load Scenario data once.

One of the drawbacks, on the other hand, is that we need to always load
this data, even if no integration tests need running.

We can try to be smart about it and check if any integration tests are
loaded.
Fix syntax error
Return last builds on each branch for /builds?branches=true

This is a hack to fix travis-ci/travis-web#123 easier. A proper solution
would be to refactor how /branches work.