Fix #165 Use Corrected CFL Criteria

A. Taflove & M. E. Brodwin
IEEE Trans. on Microwave Theory and Techniques, August 1975
Formula (7)
Show Optimal CFL in InitialiserController

- shows selected and minimum possible ratio for time step
- refactor to use log<picLog::PHYSICS> for standard sim
  output during startup
Merge pull request #371 from ax3l/fix-cfl

Fix #165 Use Corrected CFL Criteria