Update netCDF version to 4.3.19
Update NetCDFServiceImpl and HDF-based readers for netCDF 4.3.19

There are a number of differences in the group/attribute names and
values returned by 4.3.19 when compared with 4.0.x.  Some of the names
contain spaces instead of underscores and/or extra characters; for image
data arrays, the endianness may be reversed (which was actually a bug in
4.0.x).

This completes ticket #6853.
Fix NetCDFServiceTest to account for 4.3.19 upgrade
Add Unidata Maven repository and fix the committed netCDF jar

netCDF 4.3.19 is not in Maven central, so the Unidata is used instead.
Imaris HDF: revert some of the changes for netCDF 4.3.19
NetCDF service: prevent NPE when parsing attributes
Merge pull request #790 from melissalinkert/netcdf-update

Update netCDF to 4.3.19