Completed task: "Number of Issues Assigned Per Contributor".

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