[SPARK-7305] [STREAMING] [WEBUI] Make BatchPage show friendly information when...

[SPARK-7305] [STREAMING] [WEBUI] Make BatchPage show friendly information when jobs are dropped by SparkListener

If jobs are dropped by SparkListener, at least we can show the job ids in BatchPage. Screenshot:

![b1](https://cloud.githubusercontent.com/assets/1000778/7434968/f19aa784-eff3-11e4-8f86-36a073873574.png)

Author: zsxwing <zsxwing@gmail.com>

Closes #5840 from zsxwing/SPARK-7305 and squashes the following commits:

aca0ba6 [zsxwing] Fix the code style
718765e [zsxwing] Make generateNormalJobRow private
8073b03 [zsxwing] Merge branch 'master' into SPARK-7305
83dec11 [zsxwing] Make BatchPage show friendly information when jobs are dropped by SparkListener