Sawfish 1.10 SawfishConfig UI changes

Hi all,

I was thinking about refining UI of SawfishConfig for next release.

First thing was done is the removal of those bottom buttons new in Sawfish 1.9 
and replacing them with widgets on the right in SawfishConfigs main group.

See attached screenshots.

I added label, shell, link and xdg widgets for defcustoms. You may wonder why 
there's a label widget. Well the introduction text is a pure label widget and 
in conjunction with and/or widgets it can be used to prevent GtkButtons from 
growing height when theres more than one line of descriptive text (have a look 
at grow-pack defcustoms, there's one HUGE GtkButton - this can be prevented 
now). Next is using proper line-wrap in SawfishConfig and the prevention of 
those huge GtkButtons.

Comments, suggestions welcome.

Regards,
Chris