Change how the ActionManager's initialised.

Do the same as the IdentityManager, to make it easier to DI later.

Change-Id: I29e96fa04615fa86c028b384ccd26a7a53fee6cf
Reviewed-on: http://gerrit.dmdirc.com/2678
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager