API migration to new permissions model

I will fix this commit and write something more meaningful. v2 doesn't differ much from v1 in this regard.

For the moment we can use this for discussion, I jotted down a few questions that raised while I was doing this:

- How are we testing permissions work well, when permissions are in nested usergroups, etc..?
- Why is ```auth_source_ldaps``` not using ```authorized``` for anything?
- Why do we have a permission ```ipmi_boot``` under resource Hosts? I'd suggest change it to ```boot_hosts``` (it makes some things easier, and its more homogeneous with the rest)
- Why ```HostgroupClass, HostClass``` miss view/destroy permissions?
- What to do in ```os_default_template``` API controller? There's no permission for that, check permissions for ```config_templates``` maybe?
- ```LookupKeys``` have permissions like ```view_external_variables```, why? They can also be smart_class_parameters, or better yet, lookup_keys :tongue: 
- ```LookupValues``` have no permissions?
- ```Roles``` have no permissions?
- What are ```Parameter``` permissions used for? Shouldn't the permissions of the object that contains these parameters be used instead? (i.e: :view_hosts instead of :view_parameters for /api/hosts/1/parameters) That's the approach I followed with NIC interfaces.
- Regular controllers should have an ```after_filter``` to set the ```@authorizer``` variable, want me to do that?
- Are we going to auto prepend ```authorized(:whatever)``` to methods like ```search_for```, etc.. which will always clearly need it? Otherwise writing new code might get hairy, I have very mixed feelings about this.
- If not, we'll be on the lookout for the ```authorized``` scope forever?

I saw some errors not related to this that don't have an issue in redmine that I'll open tickets for them soon too:

- Users #update checks for email existence, #create does not.
- build_pxe needs some error handling
- autosign_controller returns 500 when the smart proxy is unreachable

Thanks!