Don't construct ConfigManagers.

Use a factory where available, and horrible singleton where not.

(ConfigManager was using a horrible singleton anyway, under the hood,
 so it's not that much worse)

Change-Id: I82d215bf22b68d0359fce4c33976a9bf68d2bfda
Reviewed-on: http://gerrit.dmdirc.com/3080
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager