Make Page Navigation List Widget Work in Editor for New Pages

Sometimes jQuery cached data attributes too eagerly causing the page
id read from the page element to be undefined. This lead to broken
highlighting of current page in editor. Read attribute directly
instead.
Prevent Edit Lock Conflict when Reopening Editor

Edit lock id was not purged from session store causing the first
aquire to refresh a lock that was no longer there.
Merge pull request #200 from tf/page-navigation-list-fix

Make Page Navigation List Widget Work in Editor for New Pages
Merge pull request #202 from tf/edit-lock-conflict

Prevent Edit Lock Conflict when Reopening Editor