Add handling for github issues

This adds new code to deal with issue events (only 'open' actions at this
point).

In the process I've decomposed some of the code, breaking out jobs into its own
classes that both PullRequestJob and IssueJob inherits. Also moved TrelloAPI
into its own file.

Signed-off-by: Ken Barber <ken@bob.sh>
Rename Job classes to be Trello Specific

Without this patch all of the classes dealing with performing heavy
lifting are named generically.  PullRequestJob and IssueJob and Job for
example.  These classes are fairly focused and
specific to performing the job of creating a new card on a Trello list.

This is a problem because we do not make it clear to the reader the
specific nature of these delayed job classes.

This patch addresses the problem be renaming many of the classes to
include a Trello specific name.
Remove gepetto-bot's Trello APP key from the README

This application key could be used to request user tokens and use up
our API quota.  This patch fixes the problem by removing the key from
the README.
Remove PuppetLabs::TrelloUtils module

The only method provided by this module was never being called by
anything else in the code.  It seems silly to carry the experiment
forward and confuse readers.
Merge branch 'kbarber-ticket/master/issues_support'

* kbarber-ticket/master/issues_support:
  Remove PuppetLabs::TrelloUtils module
  Remove gepetto-bot's Trello APP key from the README
  Rename Job classes to be Trello Specific
  Add handling for github issues

closes: #16