Cleanup javadocs.  This makes the following changes:
  1) Stop using doclava.  It has too many bugs (like dropping annotations).
  2) Tell javadoc not to doclint.  Java8 does it and errs if it fails.
  3) Link to appropriate third parties from javadoc.
  4) Split extensions into separate groups in ant javadoc.
  5) Cleanup code that had javadoc warnings.
Publish javadocs using jdk8, not jdk7.
Fix spacing for Struts2GuicePluginModule
Merge pull request #822 from sameb/no-doclava

Cleanup javadocs, stop using doclava