Port stylegrid-example to ExtJS 5.0.0

Several changes where needed, that have to be reviewed:
- check if "meta" is defined in Symbolizer.js. meta is undefined after editing
  an cell.
- root-Keyword in readers in RasterStyleModel.js and VectorStyleModel.js
  are now dynamically set to ExtJS5s "rootProperty" or ExtJS4s "root".
- removed defaultValue: null in symbolizer-field. It now uses the
  ExtJS-default which is "undefined"
- dynamized the test to pass with ExtJS4 and ExtJS5