build: Update grunt-jscs (formerly grunt-jscs-checker) from 0.4.4 to 0.6.1

Also switch to the new 'wikimedia' preset in jscs to make .jscsrc shorter
(but with a number of exemptions that need to be cleaned up later).

Change-Id: I836f3e96f2126f3684c3e60b7fa11de8724b5262