mongo collection names
incorrect media type
fixed NPE while adding group members
support for user-ref media type
removed descripton from group list
path constants
fixed group encoding/schema
added created/modified times to sensor
fixed identifier property name
extended track validator
fixed track creation decoding
fixed track schema
formatted schema
fixed /users/user/tracks resource
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