Complete the lookup, "data in modules" feature

In Puppet 4.0.0 the basic features for supplying data for explicit and automatic lookup were introduced. Targeting Puppet 4.2.0 the basic set of features should be completed with the following functionality:

• hiera data should be supported in modules and environments. The data structure and data files should be fully backwards compatible
• hiera configuration should support using the same backend more than once - this potentially includes making modifications that may require small changes to the current hiera.yaml configuration file to be used inside modules and environments.
• the lookup should be able to explain decision leading to a found value (or no found value)
• a command line utility should be able to do a correct lookup across all data providers (the existing hiera command line tool cannot do this)

The details of these features are described by tickets individually in this epic.

This epic supplants the earlier PUP-42 epic as this represents a fresh approach and PUP-42 led to the introduction of the binder and several of this issues in that epic are stale / irrelevant.

The fresh approach is to build a hiera-compatible implementation based on new APIs. This logic will reside in the puppet code base and be based on the data-provider API introduced in Puppet 4.0.0.