Tabbedinterface (mobile): allow URL hash to determine active tab to display

Adds ability to specify active tab with URL hash when in mobile view.  This makes the tabbed interface behaviour more consistent between desktop/mobile (part of the change from PR #2423).

I'll add a comment to #2331 that documents the low risk breaking change this introduces so we can add it to the release notes: 

* **Mobile:** URL hash panel select takes precedence over sessionStorage panel select.