Make buttons' location fixed

[Waldir Pimenta]

It would make playing less error-prone to have the buttons always at the same place.

Also, for small screens it could be interesting to make them always visible (e.g. position:fixed, bottom:0) so you could still scroll the text down if it's too long, but the buttons would be always visible from the moment the item loads.

[Waldir Pimenta]

Perhaps also make the three buttons (or at least the two explicit choice ones) the same size. This would at least make their position stable/predictable in the horizontal direction. I suspect making them all 33% wide would be the most straightforward approach (but the wrapping div would have to be max-size'd to prevent having extremely wide buttons in large screens).

[Magnus Manske]

Buttons now fixed at screen bottom, for devices with portrait orientation.

Button size should be a different issue, but it's tight enough on mobile screens as it is.

[Waldir Pimenta]

Issue #113 was marked as a duplicate of this issue.