Includes multiple changes to the shifter task to simplify and
support this:
* Use grunt.file for shifter yui 'module' detection rather than our own
70 line function
* Use grunt.util.spawn rather than our own exec for shifter
* Improve behaviour on various yui subdirectories
We have to add the 'async' depndency to npm because we are running
multiple async operations in the single task. We use async.eachSeries to
run each shifter job sequentally (else the output would be unreadable
when running async).
We also run shifter in non-recursive mode on the module directory so its
not building everything (thanks to Ryan for pointing this out!)
We've tried various approaches to lock down our dependencies and they
have been flawed because dependencies in our included packages may not
be locked down and previous attempts to do that have not been correct.
With npm shrinkwrap we lock down versions so that any npm install will
always install the exact same versions for all developers - see:
https://docs.npmjs.com/cli/shrinkwrap
(This is a lot like composer.lock for those more fluent with composer)
