Integration of vocabulary service and some major restructrure

This PR integrates vocab.met.no into the Nc_to_mmd class and includes also some rewriting.

1) There is a new folder "vocab", containing a script to fetch MMD and CF controlled vocabularies.

if needed these can be updated, if not the current vocabularies can be used
if fetching updates fails, vocabularies are not ovewritten
vocabularies contain info that are used in nc_to_mmd and add_gcmdfromcf (new)
get_vocab uses SPARQLWrapper for sparql query, as it is faster than using the REST API interface through urllib

2) Nc_to_mmd requires now to import vocab (this is added to traverse_thredds, traverseListfile.py, nc_to_mmd and mdh_modules/nc_to_mmd.py)

3) add_gcmdfromcf as been added as additional service

it reads an mmd file and adds GCMDSK keywords from CF standard name mapping through vocab
it can also just print out matches using a -p argument

4) mdh_modules/nc_to_mmd.py has some major changes

it includes CF standard names to keywords validating against the local vocab module
'latitude', 'longitude', 'time' are removed from keywords as they are not particularly significant (it can be changed eventually)
mmd elements are suffled to ease mmd validation against mmd schema
norwegian title and abstract are added to support genorge
dataset_production_status is added as it is mandatory in mmd
iso_topic_category is added as it is mandatory (removed from traverse_thredds)
spartial_representation is added to support inspire (if available)
minor correction for activity_type
licence is now more complex, but through vocab it covers an extensive combination of possibilities provided in global attributes
keywords are extended with new vocabularies (it should be revised in the future)
minor modification of keywords, so that gcmd list is not overwritten
all controlled vocabularies are now validated through vocab, so hard coded lists are removed

5) traverse_thredds

minor updates to provide collection in the right place according to MMD schema
minor update for related_information order of children
activity_type and operational status are added only if not already present (not mandatory in MMD)
iso_topic_category is moved into nc_to_mmd

steingod / mdharvest