Merge branch 'dev'

* dev:
  fixed /users/user/tracks resource
  formatted schema
  fixed track schema
  fixed track creation decoding
  extended track validator
  fixed identifier property name
  added created/modified times to sensor
  fixed group encoding/schema
  path constants
  removed descripton from group list
  support for user-ref media type
  fixed NPE while adding group members
  incorrect media type
  mongo collection names
added local GeoJSON geometry schema
renamed identifier property
fixed incorrect constant
additional validation for measurements
do not save id/created/modified for measurement values
save optional track in measurements
fixed endless recursion due incorrect method call
add track/user to created measurements
renamed identifier property
add created measurements to track
measurement encoding/decoding
throw 404 for invalid measurement identifier
throw 404 for measurements that are not in the track
catch IAE for invalid ObjectIDs
fixed get measurement by id
removed auth annotation for GET methods
activated jersey logging filter
disabled logging filter