Track tab changes and tree popups in browser history

This adds support for Back (and Forward) buttons to step through tabs in the curation tool. It also means we can share URLs that will open to a preset tab or tree, like so:

http://devtree.opentreeoflife.org/curator/study/view/pg_10/?tab=otu-mapping

http://devtree.opentreeoflife.org/curator/study/view/pg_10/?tab=trees&tree=u14ab09e0-9972-41af-880a-018c07468627g0n0

The user will see a notice if the specified tree has since been removed. Note that simple tree popups will be added to history, but more complex tree views (ie, stepping through conflicting taxa in a tree) will not.