Helpers: resetActivePageHeight now accounts for external toolbars

Fixes gh-7134
Navigation: resetActivePageHeight() on pageshow but wait for window.load

This fixes the problem whereby header and footer heights are miscalculated when
showing the initial page, because during the initial page load, pageshow
happens before window.load, meaning that the CSS may not yet be loaded,
affecting header and footer heights.

Re gh-7134