Fix PR comments including some UI tweaks and bug fixes.

Hide no annotations/notes message when annotations are still loading.
When the annotations are still loading, a 0 annotations message shows for a flash of a
second before the list loads. Avoid this by only displaying the 0 state after the
annotations have finished loading.

If selected annotation/note is deleted, default selected tab to annotation.
If a user lands on a direct link for a deleted annotation, the button to take the user
back to the list of annotations/notes should by default be for annotations.
On clearning the selection, filter annotations according to the selected tab type.

Fix broken standalone page for notes.
selectedTab was set to annotations by default, even for standalone pages.
selectedTab should be undefined for a standalone page because there are no tabs to select from.
select the annotations tab by default for the sidebar alone.

Change copy for empty annotaitons/notes state.