Make sure show is always a string

This is so we hopefully can find some bugs

gajim/common/contacts.py

@@ -65,6 +65,16 @@ class CommonContact(XMPPEntity):
         # this is contact's chatstate
         self.chatstate = chatstate
 
+    @property
+    def show(self):
+        return self._show
+
+    @show.setter
+    def show(self, value):
+        if not isinstance(value, str):
+            raise TypeError('show must be a string')
+        self._show = value
+
     def get_full_jid(self):
         raise NotImplementedError
 

gajim/common/helpers.py

@@ -420,7 +420,7 @@ def get_css_show_color(show):
         return None
     elif show in ('xa', 'dnd'):
         return 'status-dnd'
-    elif show in ('away'):
+    elif show == 'away':
         return 'status-away'
 
 def get_uf_sub(sub):