Added Customer Timers

Taking inspiration from Overcooked!, customers now get impatient and leave after a while.

12-03-2019:
Added Customer Timers.
• Customers will leave after their timer runs out, and you won't be able to complete their order.
Added card that gives a temporary shield that protect foods from hazards.
Added card and hazard that affects customer timers.
Added seventh level.
Cards that can't be played return to player's hand after mouse (or finger) is released.
Fixed bug that allowed food to be able to be placed on the same grid space as another.
Fixed bug that allowed food to travel past the grid edges.
Various other small quality improvements across the board.