Fixes #5186, #5189 - Content Host - show provisioning details and cross-link to foreman host

This commit contains a few basic changes, including:

1. Add a foreign key to katello's system to enable associating it to a foreman host
2. Add a 'Provisioning Details' tab to a katello content host
3. Add high-level information from foreman to the provisioning details.  At this time,
   this includes the information that is currently shown from foreman host list,
   such as name, status, OS, puppet environment, last puppet report, model & host group.
4. Provide cross-linking (where possible) from the katello content host to the foreman host.
   This currently supports linking to the host as well as hostgroup.

This commit does not include the logic to actually associate the katello content host
to the foreman host.  That work will be done separately.  To test this, the association
was manually done using rails console.

![provision-details-none-available](https://cloud.githubusercontent.com/assets/1319246/2830836/d411aad0-cfb2-11e3-943b-e44564d4c8d6.png)

![provisioning-details](https://cloud.githubusercontent.com/assets/1319246/2830839/da1c218a-cfb2-11e3-995c-bb8c10eba23e.png)