Add author information to card

Without this patch, while looking at the Trello board it's difficult to see who
opened a pull request.  This is a problem because I often need to find a card
that a particular user is talking about.

This patch addresses the problem by adding an avatar image of the contributor,
their full name, their company, and their email to the description of the card.
In addition, their full name is included in the card title.

As part of this change the job needs to communicate with Github to obtain the
full data about the github login who sent the pull request.

Here's what the card looks like:

![Trello Card](http://goo.gl/sNMa3)

Finally, this change set also changes the behavior of how the app matches up
events to cards that may exist on the trello board.  Without this patch applied
the entire string of the expected card title is searched for and matched.  This
is a problem because the same card should be found if the issue or pull request
title changes.  This patch addresses the problem by restricting the card
identifier to be strictly based on the repository name and issue number.  Each
job class is expected to implement a new `card_identifier` method.  The
application will search card titles and perform a substring match.