Add Fencing support

...by overriding Foreman views and controllers.
The following files are copied over from Foreman and modified for the specific use-case:
- app/assets/javascripts/staypuft/host_edit.js
- app/views/hosts/_form.html.erb
- app/views/hosts/_unattended.html.erb
So this is one place where the safe mode whitelist may need extending (for the NIC params) -- for Host, it will need to be added elsewhere.