Added Admin and Roles Fucnctionality to Apricot.Web

1. Added Roles Functionality.
2. Admin can Create New Users and Assign Roles to Them.
3. Admin Tab only Visible to Admin (Changes in _Layout.cshtml)
4. Only Admin can Create and delete a User and Change its roles .

Changes Made in Accordance with "http://www.codeproject.com/Articles/682113/Extending-Identity-Accounts-and-Implementing-Rol"