Cockpit Failed Jobs Plugin (CAM-1901)

A Cockpit plugin, which shows a list of failed jobs on start page of cockpit.
It uses [Camunda Rest API](http://docs.camunda.org/latest/api-references/rest/#job-get-jobs) to show us the latest failed jobs:

![cockpit failed jobs](https://f.cloud.github.com/assets/6114456/2294626/8e579944-a084-11e3-9dd9-bbb6538c6cbe.png)

In the **Process instance ID** column, it show us the instance id wrapped in a link which goes the latest live state of the process instance.

In the **exception** column it has the exception message which is linked to a page which shows the whole exception stacktrace.
(created based on this [ticket](https://app.camunda.com/jira/browse/CAM-1901))