(PDB-452) Adding support for storing environments

Added support for environments to the model and command wire formats.
Minor doc changes
Merge pull request #894 from senior/ticket/master/pdb-452-support-environments-in-commands

(PDB-452) Adding support for storing environments
PDB-453 Add environments to all terminii

This patch ensures that the request environment is sent to PuppetDB inside
the payloads for the object types: facts, catalogs & reports.

Signed-off-by: Ken Barber <ken@bob.sh>
PDB-453 Flatten catalog wire format

Signed-off-by: Ken Barber <ken@bob.sh>