Fixes #132 - Added a clone operation

This clones the AR, attaches clones of the
originals host_parameters and then renders the "new" action, ready for editing.

The host_parameters must not use validate_presence of :host_id when using nested attributes.
Created a hidden :nested attribute to the form to flag this behaviour...

Added Groups to puppet classes, now its possible to associate a host with a group of classes
it also allowed to setup parameters per group and override them in the host level

I've done it late at night, so who knows :)