Add animation to newly added tiles and newly generated plus tiles.

[toolness]

This issue has been migrated from mozilla/webmaker-android#1798.

It was originally written by flukeout on Mon May 11 2015 and had the following description:

We need some kind of little pop or "ba-doop!" animation for newly created tiles. Just showing them suddenly is a little jarring. Maybe a little sound might be nice as well?!

On Mon May 11 2015, thisandagain commented:

👍