Add Module Tool

This rather large commit includes all the work needed to get the `puppet
module` face in Puppet with all it's actions. I tried to break this up
into smaller commits, but it was difficult to do so and keep the
individual commits in a state that had passing specs since many changes
in shared module_tool code affected multiple actions. This code was
developed in an integration branch over a few montsh and is now being
merged back into Puppet core in the same state that shipped with Puppet
Enterprise 2.5.

The work here was done by Pieter van de Bruggen <pieter@puppetlabs.com>,
Kelsey Hightower <kelsey@puppetlabs.com> and myself.