Use store rather than groups to get focusedGroupId

Instead of going through a layer of indirection (aka the groups
service) to get the focusedGroupId use the store directly.

src/sidebar/components/sidebar-content.js

@@ -233,16 +233,20 @@ function SidebarContentController(
   // Re-fetch annotations when focused group, logged-in user or connected frames
   // change.
   $scope.$watch(
-    () => [groups.focused(), store.profile().userid, ...store.searchUris()],
-    ([currentGroup], [prevGroup]) => {
-      if (!currentGroup) {
-        // When switching accounts, groups are cleared and so the focused group
+    () => [
+      store.focusedGroupId(),
+      store.profile().userid,
+      ...store.searchUris(),
+    ],
+    ([currentGroupId], [prevGroupId]) => {
+      if (!currentGroupId) {
+        // When switching accounts, groups are cleared and so the focused group id
         // will be null for a brief period of time.
         store.clearSelectedAnnotations();
         return;
       }
 
-      if (!prevGroup || currentGroup.id !== prevGroup.id) {
+      if (!prevGroupId || currentGroupId !== prevGroupId) {
         // The focused group may be changed during loading annotations as a result
         // of switching to the group containing a direct-linked annotation.
         //

src/sidebar/components/test/sidebar-content-test.js

@@ -168,6 +168,10 @@ describe('sidebar.components.sidebar-content', function() {
       $scope = $rootScope.$new();
       store = _store_;
       store.updateFrameAnnotationFetchStatus = sinon.stub();
+      store.clearGroups();
+      store.loadGroups([{ id: 'group-id' }]);
+      store.focusGroup('group-id');
+
       ctrl = $componentController(
         'sidebarContent',
         { $scope: $scope },
@@ -491,15 +495,12 @@ describe('sidebar.components.sidebar-content', function() {
       $scope.$digest();
     });
 
-    function changeGroup() {
-      fakeGroups.focused.returns({ id: 'different-group' });
-      $scope.$digest();
-    }
-
     it('should load annotations for the new group', () => {
       const loadSpy = fakeAnnotationMapper.loadAnnotations;
+      store.loadGroups([{ id: 'different-group' }]);
+      store.focusGroup('different-group');
 
-      changeGroup();
+      $scope.$digest();
 
       assert.calledWith(fakeAnnotationMapper.unloadAnnotations, [
         sinon.match({ id: '123' }),
@@ -511,8 +512,10 @@ describe('sidebar.components.sidebar-content', function() {
 
     it('should clear the selection', () => {
       store.selectAnnotations(['123']);
+      store.loadGroups([{ id: 'different-group' }]);
+      store.focusGroup('different-group');
 
-      changeGroup();
+      $scope.$digest();
 
       assert.isFalse(store.hasSelectedAnnotations());
     });