adds message title, adds sender delete

- message now contains a second string
  which is meant for unencrypted title
  information, which can be displayed
  without e2e encryption.
- senders can now be deleted
- the same sender / token connection is
  no longer added to the database

priv/repo/migrations/20220103100336_add_message_title.exs

@@ -0,0 +1,10 @@
+defmodule Bump.Repo.Migrations.AddMessageTitle do
+  use Ecto.Migration
+
+  def change do
+    alter table :messages do
+      add :title, :string, size: 1024
+    end
+
+  end
+end