comments: PDF preview page in URL hash

* Synchronizes the currently previewed PDF page with the window.location.hash;

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: better base JS inclusion separation

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: PDF page preservation on form submission

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: notes reply-to-original-comments tweak

* Inserts a marker for the currently previewed page when replying to the
original comment.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>