This adds a new series of template hook points for augmenting the

display of the review request box. It allows for placing things

before/after/inside the summary information, before/after fields, and

before/after/inside the extra panes area (where the issue summary table

and file attachments live). This helps extensions to place additional

details without worrying about looking up specific elements and

modifying the DOM.
Documentation has been added for all the new template hook points.

Made sure the review request page properly loads.
New unit tests for all the template hooks pass.
Tested building docs and checking for generated output.