Use ExtJS utility methods.
Port stylegrid-example to ExtJS 5.0.0

Several changes where needed, that have to be reviewed:
- Edited rows are now silently commited cause they caused an error
  when setting css in the Symbolizer-column.
- root-Keyword in readers in RasterStyleModel.js and VectorStyleModel.js
  are changed to ExtJS5s "rootProperty" instead of ExtJS4s "root". This
  is not longer backwards compatible and show be fixed first.
- removed defaultValue: null in symbolizer-field. It now uses the
  ExtJS-default which is "undefined"
- removed "idchanged"-listener from RasterStyleModel.js cause it is not
  longer available in ExtJS5