Issue #2572929 by dawehner, pwolanin, mikeker, xjm, stefan.r, David_Rothstein,...

Issue #2572929 by dawehner, pwolanin, mikeker, xjm, stefan.r, David_Rothstein, hussainweb, lauriii, Wim Leers, catch, chx, alexpott: Document lack of auto-escape in theme functions and add a theme autoescape helper function