removed href for track measurements
do not load tracks to add measurements
measurement validation
more lazy loading
use UTC as default time
validate measurment values
entity caches
update modified time while adding measurments to track
invalidate cache on user change
manual, cached reference handling for phenomenons, users and sensors
adjusted creation script
Merge branch 'performance' into dev

* performance:
  adjusted creation script
  manual, cached reference handling for phenomenons, users and sensors
  invalidate cache on user change
  update modified time while adding measurments to track
  entity caches
  validate measurment values
  use UTC as default time
  more lazy loading
  measurement validation
  do not load tracks to add measurements
  removed href for track measurements