Update for mixed precision computations

[arango]

• The update includes changes to several files to allow mixed single and double precision in some applications. In single precision, we need to ensure that time and scale factors are in double precision. For example, in wrt_ini.F we have:

       real(r8) :: Fmin, Fmax
       real(dp) :: my_time, scale
  

  Recall that in single-precision the floating-point kind parameters are set in mod_kinds.F as:

          integer, parameter :: dp = SELECTED_REAL_KIND(12,300)  ! 64-bit
          integer, parameter :: r4 = SELECTED_REAL_KIND(6,30)    ! 32-bit
  # ifdef SINGLE_PRECISION
          integer, parameter :: r8 = SELECTED_REAL_KIND(6,30)    ! 32-bit
  # else
          integer, parameter :: r8 = SELECTED_REAL_KIND(12,300)  ! 64-bit
  # endif
  

• Modified routine wclock_off to report also the total profile times in the MPI communications for all nested grids (if NESTING is activated), and its total for all numerical kernels in 4D-Var applications.