Fix some nonsense in the LoggingManager.

Don't get a random Object only to toString() it later, just use strings.
Don't rely on toString() existing across different implementations.
Don't try and find a log file for servers, they don't exist.

Change-Id: Ic53754d16a7c0d4b63246000236e51080450cb50
Reviewed-on: http://gerrit.dmdirc.com/3878
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>