Fixes #746 - Generate all the Host template when click on Build to avoid...

Generate all the Host template when click on Build to avoid errors during installation.
Includes moving of template_used to Managed model so it can be used elsewhere.

This constructor is a tad strange. I would recommend making ```host_status```, ```templates_status```, ```smart_proxies_status``` return the status instead of setting instance variables. It'd make it more usable by any controller and unit tests will test and check whether methods are correct, not the object as they do now.