Fix quote and visual diff handling for page search

 * Replaced the obsolete ng-bind-html-unsafe directives in page_search
   with the new mechanism
 * Fixed a bug in page_search when quotes were not shown in detail mode
   (ng-hide / ng-show mixup)
 * Changed the handling of the "show diff" checkbox to be more consistend
   between search and viewer templates

Touches upon #807
Fixes #947