ENH: PatchParticleHistogram: add a new cloud FO

  Computes a histogram for the distribution of particle diameters
  and corresponding number of particles hitting on a given list of patches.

  A minimal example by using `constant/reactingCloud1Properties.cloudFunctions`:

  ```
  patchParticleHistogram1
  {
      // Mandatory entries (unmodifiable)
      type             patchParticleHistogram;
      patches          (<patch1> <patch2> ... <patchN>);
      nBins            10;
      min              0.1;
      max              10.0;
      maxStoredParcels 20;
  }
  ```