[SPARK-4411][WEB UI] Add "kill" link for jobs in the UI

## What changes were proposed in this pull request?

Currently users can kill stages via the web ui but not jobs directly (jobs are killed if one of their stages is). I've added the ability to kill jobs via the web ui. This code change is based on #4823 by lianhuiwang and updated to work with the latest code matching how stages are currently killed. In general I've copied the kill stage code warning and note comments and all. I also updated applicable tests and documentation.

## How was this patch tested?

Manually tested and dev/run-tests

![screen shot 2016-10-11 at 4 49 43 pm](https://cloud.githubusercontent.com/assets/13952758/19292857/12f1b7c0-8fd4-11e6-8982-210249f7b697.png)

Author: Alex Bozarth <ajbozart@us.ibm.com>
Author: Lianhui Wang <lianhuiwang09@gmail.com>

Closes #15441 from ajbozarth/spark4411.