Style buttons as a button group and make them larger

[Waldir Pimenta]

It could make sense to make div.decision also have the btn-group class, as the display of the buttons indeed makes sense as a group. For that, it would be necessary to override the float:left rule in Bootstrap for the .btn-group>.btn selector.

Furthermore (and perhaps more importantly), the buttons should be made larger (class btn-lg, as seen here), to improve the usability of the game in mobile phones.

[Magnus Manske]

Done.

[Waldir Pimenta]

Thanks! For future reference, this was done in 3e1a4d763. I added a comment to that commit regarding a minor implementation issue.