Add MiqWidget importing/exporting

Related to Bugzilla 1115106
https://bugzilla.redhat.com/show_bug.cgi?id=1115106

@gmcculloug @dclarizio @h-kataria Please Review.

Also note that the styling for the slick grid stuff is off, but I figured that could be fixed after this is in.
Also, should this be a nest class of the WidgetImporter, since that's really likely to be the only user.  e.g. `WidgetImporter::Validator`