Make new email relative to stored time

app/src/main/java/eu/faircode/email/EntityMessage.java

@@ -19,6 +19,7 @@ package eu.faircode.email;
     Copyright 2018 by Marcel Bokhorst (M66B)
 */
 
+import java.util.Date;
 import java.util.Random;
 
 import javax.mail.Address;
@@ -80,6 +81,8 @@ public class EntityMessage {
     @NonNull
     public Long received; // compose = stored
     @NonNull
+    public Long stored = new Date().getTime();
+    @NonNull
     public Boolean seen;
     @NonNull
     public Boolean ui_seen;