checked sign of kxarray update when sheared

-Update_ExB_shear_flow asks a step num
-this step num can be set to -1 when used in control
-the sign have been checked
-coherent with Hamett et al.
-the NL factor comp. is not optmized but fully detailed
-still has issue to verify McMillan et al. test

-dirty (lots of uncommented lines)
-unoptimized (could remove aux var)
-ExB factor still not working

- not working yet

-the routines have been tested with the CBC
-looks good, the ExB shear is not tested yet

-FFTW parallelized in ky and x
-local_nkx has been replaced by local_nx