Fixes #17681 - Switch to newly created taxonomy

fixes #17545 - adds UI notification support

- Initial data model for notification support, based on manageiq design.
- addes notification JSON endpoints.

Fixes #18045 - Puppet classes show up choosing only env.

After #3551 was merged, the hosts controller requires both environment
and hostgroup to be set in order to display puppetclasses.

It shouldn't be required to have both, so we should check what's
available and use it. If it's only the hostgroup or the environment, it...

Fixes #6502 - List ignored classes and environments on import

When importing environments and classes from puppet, ignored
environments and classes defined in ignored_environments.yml
aren't aparent.

This will add them to the list to import as ignored and...

Fixes #15403 - moved puppet to a concern in hosts UI controller

Fixes #17015 - Adds Key pairs controller

Fixes #17503 - Only trigger PXELoader suggestion when needed

Previously every host instantiation triggered a PXELoader suggestion,
which led to up to 3 extra queries per host loaded. This changes so that
the suggestion is only applied when a host changes it's OS.

Fixes #17487 - support sessions for api calls

- authenticated api calls save user to session and set
flag api_authenticated_session
- sessions with such flag allow posting requests without CSRF token
- api sessions exipre the same way as UI sessions
- api sessions don't store any additional data to keep the requests...

Fixes #15779 - make background processing available

fixes #17300 - accept Nic::Bond#attached_devices string inputs