Arrange tiles neatly when reloading the game

Arrange tiles neatly when reloading the game

The random positioning (which we use for one-at-a-time dealing of
tiles) was failing here, because each tile's random position was being
chosen against an empty playfield, (the tiles are being added in bulk
and the state isn't being updated between tiles). So the letters ended
up piling on top of each other.

We have a nice way to arrange non-overlapping tiles with the
shuff_tiles() function, so just call that once when doing a bulk
receive of tiles.