Add EventBus monitoring to ActionManager.

This is the first phase of migrating to an event bus based system.
See the migration doc here: http://s.dmdirc.com/actions-eventbus

The CLIENT_OPENED event is now triggered exclusively through the
event bus (and still works).

Issue: CLIENT-448
Change-Id: I3fb41a51a7c767558c72921241c9aa12fcae65d4
Reviewed-on: http://gerrit.dmdirc.com/3233
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>