Integrating composer (Fixes #45)
This adds a composer.json for all dependencies that are available and the include_path manipulations for "extlib/" that is still required because some dependencies are not available for composer.
This also replaces the include_path manipulation with simple requiring the autoload file, removes some require statements that are replaced with the autoloader of the packages and remove the replaced dependencies in extlib.
Please test it. Everything I checked is working, but I neither know all features nor using all plugins ;)