custom appications vbox only shows up when we select Custom. this cleans up UI by making it more robust and less confusing and gains  in height of contents of advanced tab in prefs window

enrich with info on how to ban domain and what else is allowed; make Close --> Cancel and Apply --> OK; FIXME: OK cb is not called.. :(

[knucles] make old sylte notifications taller so they look more like notif daemon ones and have better analogy