Add better JIRA integration

Sourcetree has become my preferred client for Git and I want to be able to use it the way I use Mylyn in Eclipse. Specifically, I want to be able to see all JIRA issues (using whatever filters I select), and then select an issue to be used for my commit message. I also want to be able to associate specific hunks of a change to an issue since a single file may actually contain changes for different issues.