Make Katello extendable by publishing Dynflow events on some actions

Trigger Dynflow actions on several places. Third-party gems/engines can subscribe
to this events and perform additional tasks.

This is a dependency for katello-foreman-engine that uses it to hook into relevant
actions to perform Foreman orchestration.

This PR includes patches for organization creation and deletion, environment
creation and deletion, user creation and deletion and content view promotion,
demotion and deletion.

The actions are grouped by headpin/katello to easier packaging. Events that occur
in both Headpin and Katello are in lib/headpin/actions, the rest is in
lib/katello/actions.