Add a listener for starting sprints

As an Administrator, I want the ability to configure a listener for starting a Sprint so that I can automate workflow events and send notifications to other teams.

This is important because our workflow goes from In Backlog > Committed > In Development > Accepted. When we start a sprint, we want to automatically commit to all issues that are In Backlog.

It's also important because we want to update issues that are linked to CRM tickets so stakeholders are aware that we've begun working on their issues.

We also want to send emails to other team members to let them know we're working on linked issues. For example: the web code team just started a sprint that includes a new web service the client team needs. We want to change the priority, and notify the client Product Manager and ScrumMaster so they can be prepared for the scrum of scrums.