PrefsComponentFactory checkboxes now have transparent backgrounds.

Doing this fixes several UI inconsistancies where the background colour
of the checkbox is incorrect, transparency solves this issue without
needing to change the background colour sindividually.

Fixes CLIENT-310

Change-Id: Ia7da36ffdfadfc2744322203d123fc6805513504
Reviewed-on: http://gerrit.dmdirc.com/2177
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/addons/ui_swing/PrefsComponentFactory.java

             final PreferencesSetting setting) {
         final JCheckBox option = new JCheckBox();
         option.setSelected(Boolean.parseBoolean(setting.getValue()));
+        option.setOpaque(false);
         option.addChangeListener(new ChangeListener() {
 
             /** {@inheritDoc} */