Misc. performance/UI improvements

@ebidel @addyosmani & co.:

This contains some tweaks/UI polish:
- The thumbnail `<img>` no longer appears behind the other items in the results page during the player -> results hero transition. (The fix was to set `position: relative` on the `<img>` so that the `z-index` set by the hero transition would be honored.)
- There's now a small delay in between clicking/tapping on items with ripples before the hero transition is kicked off. This ensure that the ripple effect has had a chance to animate a bit, resolving some jankiness due to the simultaneous animations.
- Additional pages of results are now being lazy-loaded when the user scrolls down to the second-to-last row. This is a good idea from an API efficiency perspective. It also helps mask a larger problem, tracked in #5, in which Firefox and IE 11 are both slowed down significantly each time a new page of results are displayed.
- `srcElement` -> `target` in one event handler, to ensure compatibility with modern browsers.

This closes #2