MDL-39092 JavaScript: Ignore all Moodle YUI coverage JS
MDL-39092 JavaScript: Remove all upstream YUI coverage JS files
MDL-39092 JavaScript: Ignore all upstream YUI coverage JS
MDL-39092 JavaScript: Add default Shifter configuration

The settings here ensure that -coverage.js files are not built, and that
the Shifter defaults to using the jshint configuration in the moodle root
directory.