Set Default Save location to Cloud on Snap! load

When Snap! is loaded, Snap! will now check whether a user is logged in
(via the presence of `SnapCloud.username`) and if so, the default save
location will be the cloud.

_NOTE:_ currently, I'm not able to really test this since I'm never logged
in during local development...however, I do know the code doesn't error, so
that's good. ;-)