Merging jrc_branch into master branch

Further optimization in the calculation of structure factors using PRIVATE integer rotational matrices and real translation vectors for the symmetry operators. This avoid the overhead of casting rational numbers to real values many times. Changes in Cmake to use Qparallel in ifort-release mode, adding a new version of direct_convol into FFT module, changes in the evaluation of the CPU-time using system_clock which is more adapted for parallel execution.