fixed test data script
some refactorings
moved schema validation to filter
removed schemata from providers
merged redundant code
possibility to disable validation
name and description for tracks
seperate schema prefix
path constants
sorted constants
fixed NPE for group members resource
changed mail address
added name/modified to track list (fixes #26)
Merge branch 'dev'

* dev:
  added name/modified to track list (fixes #26)
  changed mail address
  fixed NPE for group members resource
  sorted constants
  path constants
  seperate schema prefix
  name and description for tracks
  possibility to disable validation
  merged redundant code
  removed schemata from providers
  moved schema validation to filter
  some refactorings
  fixed test data script