Add preferences meta-data.

This is a conversion of all the current swing pref settings to
a new meta-data format. The plan is for the core/plugin system
to be able to parse this and generate the necessary model for
the prefs system.

Change-Id: Iea6e96db79af747c325d66a7d621b4d43b9af177
Reviewed-on: http://gerrit.dmdirc.com/3321
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>