fixes #3674 - find/replace code Host -> System and Hostgroup -> SystemGroup
fixes #3674 - rename files host.rb -> system.rb, etc
fixes #3674 - migration rename fields and tables hosts -> systems, host_id -> system_id, etc
fixes #3674 - migration to find/replace data and STI type in database, host -> system, etc
fixes #3674 - find/replace localsystem to localhost
fixes #3674 - revert system -> host for URI.parse
fixes #3674 - copy existing routes to legacy routes
fixes #3674 - modify legacy routes :path => :hosts and :as => :old_hosts
fixes #3674 - modify api v1 views to include hostgroup_id for api/hosts/:id
fixes #3674 - changed ERF51-2640: to ERF51-7324: for passing test ???