Refs #15779 - make background processing unavailable for now (#4217)

The original PR got vetted in the packaging phase and including
foreman-task as dependency of Foreman was refused. We need to rethink
our approach for getting the foreman-tasks functionality available...

fixes #18214 - accept `params` as AC::Parameters or Hash

In Rails 5, ActionController::Parameters no longer inherits from Hash
and so type checks for params.is_a?(Hash) now return false and should
accept either. (Rails commit 14a3bd5.)

fixes #18208 - replace audited-activerecord with audited (#4218)

Fixes #16752 - Extract template code from Host::Managed

Host::Managed contains a lot of code related with determining the
template that a host should have. Other Host objects such as
Host::Discovered might need that logic, without becoming a
Host::Managed....

fixes #18176 - replace clear_association_cache with reload

Reload is still necessary in Rails 5 as interfaces association will be
cached. The BMC test change is necessary to reload smart proxies
associated to the subnet after their features were altered - previously...

fixes #17545 - adds UI notification support

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

Fixes #10539 - Add default names for ifaces for oVirt CR VMs

Fixes #12547 - Added validators to interger fields

With this commit, instead of postgresql exception it will
show proper validation message for interger fields.

Fixes #17653 - Allow all parameters api to unhide values

Fixes #14714 - Make inherited Puppet Classes more apparent

To better recognize which Puppet Classes are inherited for Host
or Hostgroup they are under a sub-heading as a seperated list.