Add confirmation to new game button.

[gabrielecirulli]

This is to avoid accidental presses resetting the game.

[iirelu]

Maybe a hold-to-trigger thing? Or a double-tap.

[ezfe]

No, that isn't clear, and a confirmation works on both mobile and desktop.

[wrexroad]

This needs to be implemented somehow. The other day I had a 4096, 2048, 1024 all lined up and ready to go when my finger twiched, bumped my phone, and restarted the game. Then I was sad :(

[uberspot]

++ for a confirmation dialog. At least as a temporary solution.