Prevent rotation of cell is start or goal.
Made background of cells dark gray and borders darker gray. Reduced border size.
Fixed an oops in preventing player from rotating start and goal.
I keep oopsing. Now, the cell will rotate when you touch it /only/ when it’s not the goal and not the start.
Merge pull request #14 from zsweedyk/feature-pipeBorderTouchDisable

Aesthetic improvement and disabling of rotating start/goal