Add button for deleting jobs from queue

[h3nnn4n]

More than once I was required to either remove one pending job from Resque, or all jobs of a given class. For both cases I had to access the production server and run a custom script, which is not ideal. Based on that, this PR makes two changes:

1. Adds a dropdown with the list of all job classes in a queue and a button that removes all jobs of the selected class from the queue.
2. A button next to a pending job to delete that specific job

Here is a screenshot of how it looks:

Some notes:

• To properly support ActiveJob jobs I had to add some checks to fetch the class from the payload
• The button to remove a job will delete all jobs matching class and args. I could not find a better way to do this.

[eduardoborba]

Suggested change

	<input id="job_class" name="job_class" type="hidden" value=<%=job['class']%> />
	<input id="job_args" name="job_args" type="hidden" value=<%=job['args'].to_json%> />
	<input id="job_class" name="job_class" type="hidden" value=<%= job['class'] %> />
	<input id="job_args" name="job_args" type="hidden" value=<%= job['args'].to_json %> />

[matthewhively]

It would be nice to have this feature.