Stop grunt doing magic on subdirectories and only support --root type solution

There are various bugs floating around with grunt where it doesn't handle working in subdirectories properly.

It's my feeling is that trying to get grunt to work in subdirs is going against the grain of how its designed to work too much.

My reflections are that:

• We should stop supporting that configuration
• We should only support --root
• We should make --root work properly by:
  • Always operating in a consistent directory (moodle root)
  • Using the grunt file filtering options to filter the files passed to grunt tasks instead
• Suggested by Tim - we could have a --plugin mod_quiz option to make it easier than --root