Random session order

[pcantrell]

Some quick & dirty changes to ease (though not totally address) #85.

Background: the current UI shows just a few sessions most recent first, and the “all sessions” page shows them least recent first. This favors the very first and last sessions created, and leaves sessions in the middle a bit undervoted. The oldest ones get especially overvoted, in part because they're visible longer, and in part because you have to scroll so far on the “all sessions” page to see the newer ones.

I suspect that we'd get better data for the scheduler if we displayed a more even sampling of sessions in the UI. I made a few of the easier changes that might address that:

• Sessions home now shows a random sampling of sessions first, then recently added, then by category. Those first two are shorter than the current HP’s list.
• “All sessions” page shows most recently created first instead of least recent. (In earlier discussion, @look didn't like the idea of randomizing these because that would make it too hard to work through the list. I agree.)
• All sessions page now has a 2-column layout, so (1) less scrolling and (2) those underrepresented sessions in the middle are now right at the top of the right column.

Really wish we could have some AJAX-y think where you can vote and unvote sessions straight from the session lists by clicking a little icon or something. (There's currently no way to unvote sessions!) Alas, that's much more involved & I don't have time for it. Anyone else want to grab it?

[coveralls]

Coverage increased (+1.4%) to 92.581% when pulling a9cee07 on random-session-order into 887feb0 on master.

[coveralls]

Coverage increased (+1.4%) to 92.581% when pulling b883106 on random-session-order into 887feb0 on master.

[pcantrell]

@jcoyne Any chance I can nudge you into reviewing this? Despite long discussion above, actually relatively small changes.