webglapp.js: remove spurious invocations of initialize_objects, destroy_data and removeActorFromScene.
webglapp.js: geometries for treenode text tags are shared across all skeletons.

Also added some documentation for Skeleton.
webglapp.js: Removed another superfluous use of initialize_objects
webglapp.js: restricted connectors must show only for visible skeletons.
Comment out console.log statements in tracingtool.js