Added Qtrix::Locking module to properly synchronize qtrix ops

Execute a block only if a lock can be obtained, otherwise return
a response provided by the caller or raise an exception.  Makes
use of mlanett-redis-lock under the hood but abstracts it away
from the rest of qtrix.
Protect Qtrix module methods with locks.

Use Qtrix::Locking to synchronize certain Qtrix operations.
Have CLI give feedback when failing to acquire Qtrix locks.
Updated readme to discuss locking.