Account flair methods: allow obeying pref

This adds an optional preference to the Account flair_text and
flair_css_class methods that will return None if the user has their
flair disabled in the subreddit, to allow using these methods both for
"what flair is set to" as well as "what flair displays as".

r2/r2/models/account.py

@@ -677,10 +677,14 @@ def set_subreddit_style(self, sr, use_style):
     def flair_enabled_in_sr(self, sr_id):
         return getattr(self, 'flair_%s_enabled' % sr_id, True)
 
-    def flair_text(self, sr_id):
+    def flair_text(self, sr_id, obey_disabled=False):
+        if obey_disabled and not self.flair_enabled_in_sr(sr_id):
+            return None
         return getattr(self, 'flair_%s_text' % sr_id, None)
 
-    def flair_css_class(self, sr_id):
+    def flair_css_class(self, sr_id, obey_disabled=False):
+        if obey_disabled and not self.flair_enabled_in_sr(sr_id):
+            return None
         return getattr(self, 'flair_%s_css_class' % sr_id, None)
 
     def can_flair_in_sr(self, user, sr):