Fix NPE in reflection desire for default-package classes

Hacky fix, need a better fix.
[maven-release-plugin] prepare release grapht-0.8.1
[maven-release-plugin] prepare for next development iteration
Bump annotation processor source version (grouplens/lenskit#569)
CI build publication enhancements

- Publish test coverage to Coveralls
- Use Sonatype access token
Fix source & output encodings
Add Coveralls badge [skip ci]