Styliser tidying.

Remove ctor that was only used in tests.

Use Connection interface rather than requiring a Server.

Change-Id: Id7fa18cab27302045f60c32b478173de99a5df4d
Reviewed-on: http://gerrit.dmdirc.com/2925
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager