Include .premet additional attributes (e.g. campaigns) in UMM-G output

[juliacollins]

.premet files allow data producers to describe additional attributes, such as campaign identifiers. Extend the UMM-G output generated by metgenc to include these additional attributes if they exist in a .premet file.

The .premet structure looks like:

Container
AdditionalAttributeName
ParameterValue

Acceptance criteria: AdditionalAttributeName/ParameterValue content appears in UMM-G output.

[afitzgerrell]

once on the vpn, example premets can be downloaded from: http://staging-http.apps.int.nsidc.org/staging/SAMPLE_DATA/DUCk_project/LVIS_premet-spatial/

i have not suffixed them with DUCk...but if there's a need for me to do so, do let me know and i'll spiff 'em up.