app: Implement group management

Except group creation

app/queries/delete_group.graphql

@@ -0,0 +1,5 @@
+mutation DeleteGroupQuery($groupId: Int!) {
+  deleteGroup(groupId: $groupId) {
+    ok
+  }
+}

app/queries/get_group_details.graphql

@@ -0,0 +1,10 @@
+query GetGroupDetails($id: Int!) {
+  group(groupId: $id) {
+    id
+    displayName
+    users {
+      id
+      displayName
+    }
+  }
+}

app/queries/list_users.graphql

@@ -8,3 +8,9 @@ query ListUsersQuery($filters: RequestFilter) {
     creationDate
   }
 }
+query ListUserNames($filters: RequestFilter) {
+  users(filters: $filters) {
+    id
+    displayName
+  }
+}