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
Add attributes to whitelist for Safemode::Jail
Show expose lanplus as a boolean