Better set helper setup and cleanup machinery.
Get rid of .add_helper_async().
Remove unnecessary .add_helper() yields.
Merge branch 'feature/issue-668-better-test-helper-setup' into develop
Use wheels for Travis builds where available. (@Hodgestar)
Merge branch 'develop' into feature/issue-669-calculator-demo-app
using self.add_helper() (thanks @hodgestar!)