org-agenda.el: Allow to move backward/forward blocks

org-agenda.el: Allow to move backward/forward blocks

* org-agenda.el (org-agenda-find-same-or-today-or-agenda): Use
`org-agenda-backward-block'.
(org-agenda-backward-block): Renamed and rewritten from
`org-agenda-goto-block-beginning'.
(org-agenda-forward-block): New command.
(org-agenda-mode-map): Remap `backward-paragraph' and
`forward-paragraph' to `org-agenda-backward-block' and
`org-agenda-forward-block' respectively.

Thanks to Bart Bunting for raising this.