do not call gtkgui_helpers functions in common folder. Also fix a traceback when trying to view systray tooltip

src/common/helpers.py

@@ -896,7 +896,6 @@ def get_notification_icon_tooltip_text():
 	elif len(accounts) == 1:
 		message = accounts[0]['status_line']
 		message = reduce_chars_newlines(message, 100, 1)
-		message = gtkgui_helpers.escape_for_pango_markup(message)
 		text = _('Gajim - %s') % message
 	else:
 		text = _('Gajim - %s') % get_uf_show('offline')

src/statusicon.py

@@ -52,6 +52,8 @@ class StatusIcon(systray.Systray):
 		if not gajim.interface.systray_enabled:
 			return
 		text = helpers.get_notification_icon_tooltip_text()
+		#FIXME: if you do that, import gtkgui_helpers
+		text = gtkgui_helpers.escape_for_pango_markup(text)
 		self.status_icon.set_tooltip(text)
 		if gajim.events.get_nb_systray_events():
 			state = 'message'

src/tooltips.py

@@ -260,6 +260,7 @@ class NotificationAreaTooltip(BaseTooltip, StatusTable):
 		self.table.set_property('column-spacing', 1)
 
 		text = helpers.get_notification_icon_tooltip_text()
+		text = gtkgui_helpers.escape_for_pango_markup(text)
 		
 		self.add_text_row(text)
 		self.hbox.add(self.table)