Upgrade ant version and re-write javadoc build targets to use improved <javadoc>task

Version 1.10.6 of ant will enhance the <javadoc> task in order to understand some of the module-aware switches introduced by Java 9. Currently, our javadoc targets work around the limitations of the <javadoc> task by running javadoc via the <java> task. We should upgrade our version of ant and re-write the javadoc targets to take advantage of the improvements introduced by ant 1.10.16 (see https://dist.apache.org/repos/dist/dev/ant/RELEASE-NOTES-1.10.6.html). I imagine this work will occur in 3 phases:

1) Upgrade the Jenkins scripts to require ant 1.10.6.

2) Upgrade our build scripts to require ant 1.10.6.

3) Re-wire our javadoc targets.