Limit jobs to 10 minutes and enable heroku logging

Without this patch the default limit for jobs is in effect.  This could
cause the worker process to exceed the number of inexpensive hours
available in Heroku.  This patch addresses the problem by limiting jobs
to 10 minutes.  In addition, the retry count is extended to 5 from 3.

This patch also makes sure the worker process sends log messages to
STDERR so that Heroku picks them up and makes them available via `heroku
logs`.
Add Job classes for Closed and Reopened Pull Requests

Without this patch the events generated when a pull request is closed or
reopened are ignored by the application.  This is a problem because I
need an easy way to see what happens when a job is queued up from a
logging point of view.  Closing and reopening a pull request is an easy
way to generate some events.

This patch addresses the problem by subclassing the main PullRequestJob
with specific PullRequestReopenedJob and PullRequestCLosedJob classes.
The classes override the perform instance method called by the
DelayedJob worker process.