Rewrite function that builds form data for app environment roles form.

- Adds a property to ApplicationRole model so that it knows its related
  EnvironmentRole models.
- Rewrite the form data builder in the routes file so that it loops the
  application members and their environment roles to build the data
  structure.

atst/domain/environments.py

@@ -113,15 +113,6 @@ class Environments(object):
                 environment=environment, user=member, new_role=new_role
             )
 
-    @classmethod
-    def get_members_by_role(cls, env, role):
-        return (
-            db.session.query(EnvironmentRole)
-            .filter(EnvironmentRole.environment_id == env.id)
-            .filter(EnvironmentRole.role == role)
-            .all()
-        )
-
     @classmethod
     def revoke_access(cls, environment, target_user):
         EnvironmentRoles.delete(environment.id, target_user.id)