[SPARK-12149][WEB UI] Executor UI improvement suggestions - Color UI

Added color coding to the Executors page for Active Tasks, Failed Tasks, Completed Tasks and Task Time.

Active Tasks is shaded blue with it's range based on percentage of total cores used.
Failed Tasks is shaded red ranging over the first 10% of total tasks failed
Completed Tasks is shaded green ranging over 10% of total tasks including failed and active tasks, but only when there are active or failed tasks on that executor.
Task Time is shaded red when GC Time goes over 10% of total time with it's range directly corresponding to the percent of total time.

Author: Alex Bozarth <ajbozart@us.ibm.com>

Closes #10154 from ajbozarth/spark12149.