Add unsubscribe link to changeset notification mails

app/views/changesets/_heading.html.erb

@@ -0,0 +1,15 @@
+<% title = changeset.tags["comment"].to_s.presence || t(".title", :id => changeset.id) -%>
+<div class='mb-3'>
+  <div class="row">
+    <div class="col-auto">
+      <%= user_thumbnail changeset.user %>
+    </div>
+    <div class="col">
+      <h2><%= link_to title, changeset_path(changeset) %></h2>
+    </div>
+  </div>
+
+  <small class='text-muted'>
+    <%= t(".created_by_html", :link_user => link_to(changeset.user.display_name, user_path(changeset.user)), :created => l(changeset.created_at, :format => :blog)) %>
+  </small>
+</div>

app/views/changesets/no_such_entry.html.erb

@@ -0,0 +1,5 @@
+<% content_for :heading do %>
+  <h1><%= t ".heading", :id => h(params[:id]) %></h1>
+<% end %>
+
+<p><%= t ".body", :id => h(params[:id]) %></p>

app/views/changesets/subscribe.html.erb

@@ -0,0 +1,12 @@
+<% content_for :heading do %>
+  <h1><%= t ".heading" %></h1>
+<% end %>
+
+<%= render :partial => "heading", :object => @changeset, :as => "changeset" %>
+
+<%= bootstrap_form_tag do |f| %>
+  <% if params[:referer] -%>
+  <%= f.hidden_field :referer, :value => params[:referer] %>
+  <% end -%>
+  <%= f.primary t(".button") %>
+<% end %>

app/views/changesets/unsubscribe.html.erb

@@ -0,0 +1,12 @@
+<% content_for :heading do %>
+  <h1><%= t ".heading" %></h1>
+<% end %>
+
+<%= render :partial => "heading", :object => @changeset, :as => "changeset" %>
+
+<%= bootstrap_form_tag do |f| %>
+  <% if params[:referer] -%>
+  <%= f.hidden_field :referer, :value => params[:referer] %>
+  <% end -%>
+  <%= f.primary t(".button") %>
+<% end %>