add the option to allow the title of the window to change

it can be configured through the advanced config window
fix ticket #184

src/common/config.py

@@ -91,6 +91,7 @@ class Config:
 		'usegpg': [ opt_bool, False ],
 		'lognotusr': [ opt_bool, True ],
 		'lognotsep': [ opt_bool, True ],
+		'change_title': [ opt_bool, True ],
 	}
 
 	__options_per_key = {

src/roster_window.py

@@ -1381,7 +1381,7 @@ class Roster_window:
 		return
 
 	def show_title(self):
-		change_title_allowed = True # FIXME: add in expert settings
+		change_title_allowed = gajim.config.get('change_title')
 		if change_title_allowed:
 			start = ''
 			if self.nb_unread > 1: