Issue #2047227 by StephaneQ, SeanKelly, richardj: Update templates to leverage support for the Twig {% trans %} tag extension.

Issue #2013094 by pwieck, Cottser: Remove unnecessary template_preprocess() reference from all Twig files

Issue #1363112 by mparker17, mgifford, tlattimore, Jacine, dcmouyard, bowersox, ry5n, ahdiaz: Simplify names of 'element-x' helper classes.

Issue #1898428 by joelpittet, shanethehat, Floydm, gillbates, steinmb, artis, Cottser, gnuget: locale.module - Convert theme_ functions to Twig.