Preserve taskboard scroll position on page refresh

Autoreferesh isn't cool...

You know what's cool?

A billion autorefresh.

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1) Preserves `$("#taskboard").scrollTop()` in localStorage.
2) Loads and uses this value from localStorage if the URL hash contains `extensionSession=1`

^^ The purpose of 2) is to ensure that navigating to the taskboard via
hyperlink or bookmark will not trigger an auto-scroll to a
previously-stored `scrollTop`.