LayerTree widget fires togglekml events

This commit makes the LayerTree widget fire "togglekml" events instead of itself add/remove the vector layer.
Add a showKMLIn2D option to LayerTree plugin

The LayerTree plugins listen to "togglekml" events from the LayerTree widget. If "showKMLIn2D" is true the "togglekml" listener adds/removes the KML features to/from the 2D map. Otherwise, it does nothing.
GEarth plugin destroys KML layer on panel close
Ext.data.Store:each is safe to removal
Merge pull request #443 from elemoine/kml-3d-only

KML using the layertree