SSN linkers
Added SSN resources and properties
link all measurements for a track
Merge branch 'ssn' of https://github.com/car-io/car.io-server into ssn

* 'ssn' of https://github.com/car-io/car.io-server:
  Added SSN resources and properties
Added DUL ontology resources and properties.
Added DUL and SSN ontologies
removed unused constants
Added licencse headers
Merge branch 'ssn' of https://github.com/enviroCar/enviroCar-server into ssn
Fix of import on DUL
DBPedia links added
rdfs prefix
removed unused variable
SSN and DUL prefixes
ssn:observedProperty
measurements described with SSN (fixes #73)
Merge branch 'ssn' of https://github.com/enviroCar/enviroCar-server into ssn

* 'ssn' of https://github.com/enviroCar/enviroCar-server:
  DBPedia links added
  Fix of import on DUL
moved DUL & SSN to vocab package
dbpedia linking for phenomenons Fixes #81
Sensor SSN linker added.