#19 Add scrollbar and/or more subtrees to prefs window

[Todd Vierling]

The preferences are growing again under OpenGaim's
watch, and it may be a good idea now to reduce clutter
by implementing one or more of a few possible things....

* add a scrollbar to the prefs window, thus allowing it
to be resized (relates to RFE 923110)

* add more subtrees, or perhaps deeper subtrees, for
"advanced" options that most users will not care to
edit -- perhaps even an "advanced" subtree all its own