Remove unused imports for shower front simulation

Use shorter form for random value between 0 and 1.
Prepare signal transport time for new class.
Add a new subclass of BaseSimulation

This is meant as an extra step between the Base simulations
and the groundparticles and shower front simulations.
It contains common functions used to simulate the response of the
HiSPARC detectors.
For now it contains GPS uncertainty, transport time, mip response.