Make notifications single instance

src/main/AndroidManifest.xml

@@ -77,7 +77,7 @@
         </activity>
         <activity android:name=".ui.activity.ManageAccountsActivity" />
         <activity android:name=".ui.activity.UserInfoActivity" />
-        <activity android:name=".ui.activity.NotificationsActivity" />
+        <activity android:name=".ui.activity.NotificationsActivity" android:launchMode="singleInstance"/>
         <activity android:name=".ui.activity.ParticipateActivity" />
         <activity android:name=".ui.activity.ActivitiesListActivity"/>
         <activity android:name=".ui.activity.FolderSyncActivity" />