Travis: Initiating build for commit '055cb7a8b10d4e1f9949b8346fb7986ae1409920' on branch 'master': Merge pull request #6024 from piwik/composer_autoloader

Switch to composer for autoloading. Add Factory base type for factory types that create classes by string ID and fix bug in those classes where exceptions were not thrown on invalid class name (instead a fatal error ocurred).