Move some logic from ConfigManagers.

Make the IdentityManager responsible for adding the initial
identities to a ConfigManager.

Change-Id: I91520e208b06d40385729b4d7adee8bb7f1141cb
Reviewed-on: http://gerrit.dmdirc.com/3083
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>