Properly filter Reflections output in Application.getTypesAnnotatedWith

Fixes a bug in `Application.getTypesAnnotatedWith()` where the Reflections query was not being properly filtered by the `packageName` specified.

The fix makes use of the `Reflections(prefix, scanners)` convenience constructor for properly specifying the prefix + scanners.

See [Lighthouse #642](https://play.lighthouseapp.com/projects/82401-play-20/tickets/642) for a report of a manifestation of the problem.