rtftok: add static array that maps between rtf and ooxml math tokens

Change-Id: I7e27115ec35ce4209b7c92951919312267754742
rtftok: OPEN_M_TOKEN -> RTFTokenizer::lookupMathKeyword()

Change-Id: I60d0e65d0e7f37b2d5cded64cee1270c51ed5b3d