Removed the BundleResourceRetriever, FileRetriever, and JarRetriever; replaced them with a DefaultRetriever which gets returned by the RetrieverFactory if there's no specific retriever for URLs
Removed the obsolete FileRetrieverTest
Added dataset to exported packages
Changed the ImageRegistry to use platform URLs instead of bundleresource URLs (Fixes #14)
Added the urlStreamHandlers extension point to the core plugin, which allows developers to register custom URL protocol handlers. Added two custom URL protocol handlers for reading a default system icon for a given file (or extension).
Removed the ICatalogLabelProvider interface and its associated extension point catalog.ui.labelProviders. Replaced it with the ability for ICatalogTreeNode implementations to return a URL for their icon, and added the default icon URLs to the AbstractCatalogTreeNode.
Simplified creation of systemicon URL
Added better error handling to custom URL stream handlers
Added directory catalog, which is a catalog that reads layers from a given directory