Fixes #5459 - Add zanata.xml file for RH translations
Correctly use V2 API namespace
Fixes #5781 - Change controller name to DiscoveredHostsController

This fixes the awkward english around 'discover(s)' and updates the
API to match, using 'discovered_host(s)' across the board.
Fixes #5589 - Add a prefix to hostnames to avoid hostnames beginning with a digit
Bump to 1.3.0.rc3
Removing legacy foreman plugin, updating readme

Most of the changes are from lzap, I just structured it better :)