Add plugin manager based upon SimpleCI's plugin manager. Now we've got some progress on actually allowing people to track issues. Bugs, Stories, and Features are now extending "IssueType", a barebones class that gives you the ability to create a type of issue. Examples are tickets for using DirectIssues as a ticket tracker. We may implement some sort of system like that later on, for major customization reasons, to broaden the range of our users.