Make tables sortable

[fasiha]

D3's design of putting data into the DOM for later selection and processing is fantastic. I can do this right now in the Javascript console:

d3.select('tbody').selectAll('tr').sort(function(a, b) {
    return -(a.noteSortKeyFact - b.noteSortKeyFact) /
               (_.max(_.pluck(revlogTable, 'noteSortKeyFact')) * 2) +
           (a.ease - b.ease);
});

to sort the reviews table so that lower ease (review result) is at the top, and for reviews at the same ease, the higher noteSortKeyFact (in this case, the kanji number) comes first, so I see the ones I failed and most recently learned at the top. THAT was easy! (http://bl.ocks.org/mbostock/3719724 inspiration)