Make URLBuilders optional in text labels.

All existing usages will omit a URL Builder, but there doesn't appear to be
any places where it's actually needed.

Change-Id: Ic803610ec59bc5818dab83558889f2f99d312050
Reviewed-on: http://gerrit.dmdirc.com/3111
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>