Added volatile to uint8_t status

Since the status of the bartender can be changed by an ISR it is
best to make it volatile to make sure that we are loading it
from memory everytime we request it and not using a register cached
value.
Added starting logic for stop command

Added the bartender_stop() and bartender_reset() inorder to implement
the stop command. This command is for safety reasons. A button on the
order sceen of the app will have a stop button in case anything were
to happen while pouring a drink.
Implemented queue_clear()

This will clear all the values in the queue.
Clear the queue if the command is CMD_STOP

Make sure that the queue is cleared if the command recieved is
CMD_STOP. The bartender functions should not respond if the status
is STATUS_STOPPED.