Add support for additional netcdf datasets

Loading the 'mueglitz2010.nc' dataset raises the following problems.

1. netcdf-4 is currently not supported by the 'netcdfjs' library
2. once converted to classic netcdf-3 the following warnings and exceptions are raised:

loading netcdf raster image source
6624695e1e3490a3bd36.js:1 ignoring unknown dimension 'x'
6624695e1e3490a3bd36.js:1 ignoring unknown dimension 'y'
6624695e1e3490a3bd36.js:1 ignoring unknown dimension 'string13'
6624695e1e3490a3bd36.js:1 ignoring unknown dimension 'string11'
6624695e1e3490a3bd36.js:1 ignoring unknown dimension 'string10'
6624695e1e3490a3bd36.js:1 unable to detect lat/lon dimension size - ignoring data set
6624695e1e3490a3bd36.js:1 Uncaught (in promise) TypeError: Cannot read property 'dateRange' of undefined
    at new t (6624695e1e3490a3bd36.js:1)
    at 6624695e1e3490a3bd36.js:1
    at d (7358a14d15efc9acfde3.js:2)
    at Generator._invoke (7358a14d15efc9acfde3.js:2)
    at Generator.S.forEach.t.<computed> [as next] (7358a14d15efc9acfde3.js:2)
    at r (7358a14d15efc9acfde3.js:2)
    at l (7358a14d15efc9acfde3.js:2)