Clean up javadoc warnings

Previous javadoc run would yield tons of errors and warnings. I cleaned up the javadoc or removed it if it was deemed unnecessary.

TEST
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1. generate the javadoc: ```buildr clean doc```
2. Open up ```target/doc/index.html``` in your browser. Check a few classes. Like ```CandlepinParam``` to see that the code example shows up correctly. Also look at others like AuthInterceptor, EventCurator, Cdn, etc.