Add sign out

app/src/main/java/com/hippo/ehviewer/client/EhUtils.java

@@ -115,6 +115,12 @@ public class EhUtils {
         }
     }
 
+    public static void signOut(Context context) {
+        EhApplication.getEhCookieStore(context).signOut();
+        Settings.putAvatar(null);
+        Settings.putDisplayName(null);
+    }
+
     public static boolean hasSignedIn(Context context) {
         return EhApplication.getEhCookieStore(context).hasSignedIn();
     }