Doc: Update online documentation template

Doc: Update online documentation template

Update the online documentation template with following fixes:

   - Improve responsivess for narrow screens: TOC and sidebar
     now collapse into drop-down menus
   - React to hashchange events: When the user edits the anchor
     tag in URL and presses enter, the page is scrolled
     correctly to bring the selected section title into view.
   - Handle Ctrl and Meta keys correctly
   - Improve colors for target section highlighting
   - Minor CSS fixes

Task-number: QTWEBSITE-634
Task-number: QTWEBSITE-657
Change-Id: I7221f38cf4988497f0f24ee66e62b7b7d770a121
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>