Removal of FileSet, bundler refactoring, class renaming and start of XML and HTML bundlers

@dchambers one for you to review when you get a sec.

- removing Bundler FileSets and using getFiles on AssetAccessor instead
- removing observer stuff from FileSets
- various renames of Interfaces and classes
- removing the PathMatcher and moving the AssetFile creation on to the AssetFileFactory
- adding XML and HTML bundlers to get AspectBundling test to pass
- using the plugin locator to find the bundlers