Allow travis failures

This PR has some really minor code changes, but some quite significant CI implications. Namely:
- No longer relies on builds passing in travis because the failures are inscrutable and **do not represent the state of the application**
- Switches on javascript error reporting and in turn fixes invalid licensing application json (see [app/controllers/backdrop_stub_controller.rb](app/controllers/backdrop_stub_controller.rb) and [features/backdrop_stub_responses/licensing_applications.json](features/backdrop_stub_responses/licensing_applications.json)


removes slimmer conf, as it seemed to be setting it up in an errant manner for travis