show sync username in prefs screen

aqt/preferences.py

@@ -83,11 +83,13 @@ class Preferences(QDialog):
         if not self.prof['syncKey']:
             self._hideAuth()
         else:
+            self.form.syncUser.setText(self.prof.get('syncUser', ""))
             self.connect(self.form.syncDeauth, SIGNAL("clicked()"),
                          self.onSyncDeauth)
 
     def _hideAuth(self):
         self.form.syncDeauth.setVisible(False)
+        self.form.syncUser.setText("")
         self.form.syncLabel.setText(_("""\
 <b>Synchronization</b><br>
 Not currently enabled; click the sync button in the main window to enable."""))

designer/preferences.ui

@@ -243,6 +243,13 @@
                </property>
               </widget>
              </item>
+             <item>
+              <widget class="QLabel" name="syncUser">
+               <property name="text">
+                <string/>
+               </property>
+              </widget>
+             </item>
              <item>
               <spacer name="horizontalSpacer_2">
                <property name="orientation">