- fixed issue with code (no parser) loading in assetManager
- fixed specs and implementation for gracefull failure to load resources
- further cleanups of assetManager & specs:
 * full url is used for uri for http & https resources
 * moved data files used for tests to data folder
 * added test for resource unloading (removing from cache)
 * small cleanups in assetManager (less verbosity for console messages)