[FEATURE] Adding parallel states to the Sherpa State Machine

[Kalamar136]

PROBLEM
There are some set of Sherpa actions which could be executed concurrently, or which the order of execution doesn't matter. There could also be subsystems of the Sherpa framework that execute independently.

SOLUTION
Pytransitions already supports parallel states for its state machine. Their implementation could be extended to Sherpa and Sherpa actions