Issue #2828494 by thpoul, Wim Leers, mlewand, tstoeckler, xjm, Tade0: Update CKEditor library to 4.6

Issue #2239419 by thpoul, Wim Leers, webchick, maczizek, xjm, mlewand, Jeff Burnz, tstoeckler, Tade0, Bojhan, yoroy, tkoleary, darketaine, hass, sun, maxilein, nod_, alexpott, Feuerwagen, oleq: Include CKEditor's AutoGrow plug-in