Fixes #17681 - Switch to newly created taxonomy

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.)

Refs #17653 - fix typo in show_hidden_parameters and add tests

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....

Refs #17653 - add show_hidden to apidoc

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 #17844 - unify test mail js code

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 #17653 - Allow all parameters api to unhide values