Fixes #2232 - speed up Host view via AJAX

I split off the heavy queries to AJAX loading so that the host view is presented while the server is still looking up various details.
1. Created issue #7519 to extract these (and other related) strings
2. There are 2 parts to handling the errors - if the server throws an exception, the relevant message is displayed by the [app controller](https://github.com/theforeman/foreman/blob/develop/app/controllers/application_controller.rb#L302/) as a valid response. If the request results in an error status, the [JS code](https://github.com/theforeman/foreman/blob/develop/app/assets/javascripts/application.js#L94) displays the error.