Update internal ROMS NetCDF module

[arango]

In preparation to parallel IO, I added new generic routines to mod_netcdf.F to facilitate manipulations of NetCDF data. Usually, several NetCDF library calls are required to inquire and read dimensions or variables. The new routines provide a single interface for such operations for non-tiled operations. This also facilitates error catching during IO in distributed-memory since all the internal variables are now broadcasted to all the members of the MPI group. This will be obvious when parallel IO in the future future. I will slowly clean all the NetCDF routines that are used in ROMS to manipulate IO.