Completed task: "Number of Issues Opened Per Contributor"

This pull request addresses the following issues:

* #16: Create server route for querying issues opened per contributor
* #17: Parse issues opened per contributor data before sending to client
* #18: Create controller for handling issues opened per contributor data on client
* #19: Create factory for getting issues opened per contributor data on client from server
* #20: Create partial for displaying issues opened per contributor data on client

The number of issues opened per contributor page is located at `/#/issues_opened` URL in the browser which hooks to the `/api/issues_opened` endpoint on the server. User must specify the exact repository owner and repository name (case insensitive) before the page displays the number of issues opened per contributor for the repository.