Create 'v2' get notifications route

Return multiple notifications for a service.
Choosing a page_size or a page_number is no longer allowed.
Instead, there is a `next` link included with will return the
next {default_page_size} notifications in the sequence.

Query parameters accepted are:

 - template_type: filter by specific template types
 - status: filter by specific statuses
 - older_than: return a chronological list of notifications older
   than this one. The notification with the id that is passed in
   is _not_ returned.

Note that both `template_type` and `status` can accept multiple
parameters.  Thus it is possible to call
`/v2/notifications?status=created&status=sending&status=delivered`

app/v2/notifications/get_notifications.py

@@ -1,7 +1,8 @@
-from flask import jsonify
+from flask import jsonify, request, url_for
 
 from app import api_user
 from app.dao import notifications_dao
+from app.schemas import notifications_filter_schema
 from app.v2.notifications import notification_blueprint
 
 
@@ -14,9 +15,30 @@ def get_notification_by_id(id):
     return jsonify(notification.serialize()), 200
 
 
-@notification_blueprint.route("/", methods=['GET'])
+@notification_blueprint.route("", methods=['GET'])
 def get_notifications():
-    # validate notifications request arguments
-    # fetch all notifications
-    # return notifications_response schema
-    pass
+    data = notifications_filter_schema.load(request.args).data
+
+    paginated_notifications = notifications_dao.get_notifications_for_service(
+        str(api_user.service_id),
+        filter_dict=data,
+        key_type=api_user.key_type,
+        personalisation=True,
+        older_than=data.get('older_than')
+    )
+
+    def _build_links(notifications):
+        _links = {
+            'current': url_for(".get_notifications", **request.args.to_dict(flat=False)),
+        }
+
+        if len(notifications):
+            next_query_params = dict(request.args.to_dict(flat=False), older_than=notifications[-1].id)
+            _links['next'] = url_for(".get_notifications", **next_query_params)
+
+        return _links
+
+    return jsonify(
+        notifications=[notification.serialize() for notification in paginated_notifications.items],
+        links=_build_links(paginated_notifications.items)
+    ), 200