Display page for hosts

(note - similar to hostgroups display as on this other pull request - https://github.com/theforeman/foreman/pull/1742)

Adds a new display action for hosts. Some host details cannot be viewed by a user with edit permissions as they are only shown on the edit page. This creates a display action and view, which renders the edit page with all fields disabled and buttons removed so a user with view permissions can see the page but not edit it. The display button is added next to the edit button on the show page of a host. 

![screen shot 2014-08-21 at 3 51 39 pm](https://cloud.githubusercontent.com/assets/7310311/4173356/1f57a970-3559-11e4-9073-8ea659a7e6d7.png)

![screen shot 2014-08-21 at 3 52 29 pm](https://cloud.githubusercontent.com/assets/7310311/4173358/263b5318-3559-11e4-926d-1556d0a310a4.png)