+ WIP: ! Load TILESHEETS in advance. No redundant loading!

! Load TILESHEETS in advance. No redundant loading!
Loading images is QUICK.
Loading tile sprites is SLOW.
! MySprites' extra bulk adds to the wait.

! Even loading EMPTY TILES is slow.
First, use empty streamlined MySprites.
If that doesn't work, make and use IgnoreSprite.