Diag decimation prototype, requesting in diag_table

- This update allows using non-native and decimated diagnostics
  as well as their combinations. E.g., it works for a diag_table as shown below.
- I have to
      validate with a full diagnostics
      validate individual diagnostics make sense
      study the memory foot print to make sure the decimate rotuines have no leak (due to extensive use of fortran pointers)
- Also we have to work on an averaging rather than sub-sampling of the fields as is done in this prototype

OM5p5
1900 1 1 0 0 0
"ocean_hour",            0, "days",   1, "days", "time"
"ocean_model",   "tos",          "tos",              "ocean_hour",         "all", "mean", "none",2
"ocean_model",   "thetao",       "thetao",           "ocean_hour",         "all", "mean", "none",2
"ocean_model",   "umo",          "umo",              "ocean_hour",         "all", "mean", "none",2
"ocean_model",   "vmo",          "vmo",              "ocean_hour",         "all", "mean", "none",2
"ocean_model",   "volcello",     "volcello",         "ocean_hour",         "all", "mean", "none",2 # Cell measure for 3d data
"ocean_hour_d2",            0, "days",   1, "days", "time"
"ocean_model_d2",   "tos",          "tos",              "ocean_hour_d2",         "all", "mean", "none",2
"ocean_model_d2",   "thetao",       "thetao",           "ocean_hour_d2",         "all", "mean", "none",2
"ocean_model_d2",   "umo",          "umo",              "ocean_hour_d2",         "all", "mean", "none",2
"ocean_model_d2",   "vmo",          "vmo",              "ocean_hour_d2",         "all", "mean", "none",2
"ocean_model_d2",   "volcello",     "volcello",         "ocean_hour_d2",         "all", "mean", "none",2 # Cell measure for 3d data
"ocean_hour_z",            0, "days",   1, "days", "time"
"ocean_model_z",   "thetao",       "thetao",          "ocean_hour_z",         "all", "mean", "none",2
"ocean_model_z",   "umo",          "umo",             "ocean_hour_z",         "all", "mean", "none",2
"ocean_model_z",   "vmo",          "vmo",             "ocean_hour_z",         "all", "mean", "none",2
"ocean_model_z",   "volcello",     "volcello",        "ocean_hour_z",         "all", "mean", "none",2 # Cell measure for 3d data
"ocean_hour_z_d2",            0, "days",   1, "days", "time"
"ocean_model_z_d2",   "thetao",       "thetao",          "ocean_hour_z_d2",         "all", "mean", "none",2
"ocean_model_z_d2",   "umo",          "umo",             "ocean_hour_z_d2",         "all", "mean", "none",2
"ocean_model_z_d2",   "vmo",          "vmo",             "ocean_hour_z_d2",         "all", "mean", "none",2
"ocean_model_z_d2",   "volcello",     "volcello",        "ocean_hour_z_d2",         "all", "mean", "none",2 # Cell measure for 3d data