Removed cron jobs table from role and env page. Added cron job summary to job page.

Updated getTasksQuery to not throw an exception when requesting a cron job with no tasks.

Testing Done:
Tested on local laptop.
./gradlew clean build.
./pants src/test/python:all -vxs

Bugs closed: AURORA-384

Reviewed at https://reviews.apache.org/r/21250/