Made WinJS amd modules free of global WinJS, now the wrappers (WinJS.js, base.js, ui.js) are the only things which publish the WinJS global, this enables SxS WinJS.
Restructured grunt requirejs task options to have defaults for most of them and only specify options
where we need to override.

Then created onefile task which can be used to build a single-file build for any single module with
all of its dependencies (e.g. "grunt onefile:WinJS/Promise" or "grunt onefile:WinJS/Controls/AppBar").

Used onefile task to build base.js and the single-file WinJS.js because those are canonical instances.
Added ./ to the beginning of excluded module
Merge pull request #459 from spankyj/require-build

Making WinJS global optional and adding 'onefile' grunt task