Add Admin System Emails view & first system email

Admins need to be able to see what a particular System Email looks like
with dummy data.

Also adding the first system email to be managed: the proposal
notification digest.

In case the current admin doesn't have any Notifications from
 ProposalNotifications there will be a crash. We'll solve this in later
 PR's with a system to "inject" sample text in email templates without
 having to generate records in the database.

app/controllers/admin/system_emails_controller.rb

@@ -1,7 +1,22 @@
 class Admin::SystemEmailsController < Admin::BaseController
 
+  before_action :load_system_email, only: [:view]
+
   def index
     @system_emails = %w(proposal_notification_digest)
   end
 
+  def view
+    case @system_email
+    when "proposal_notification_digest"
+      @notifications = Notification.where(notifiable_type: "ProposalNotification").limit(2)
+      @subject = t('mailers.proposal_notification_digest.title', org_name: Setting['org_name'])
+    end
+  end
+
+  private
+
+  def load_system_email
+    @system_email = params[:system_email_id]
+  end
 end

app/views/admin/system_emails/index.html.erb

@@ -20,8 +20,6 @@
       <td class="text-right">
         <%= link_to t("admin.shared.view"), admin_system_email_view_path(system_email),
                                             class: "button hollow" %>
-        <%= link_to t("admin.shared.preview"), admin_system_email_preview_path(system_email),
-                                               class: "button" %>
       </td>
     </tr>
   <% end %>

app/views/admin/system_emails/view.html.erb

@@ -0,0 +1,36 @@
+<%= back_link_to admin_system_emails_path %>
+
+<h2><%= t("admin.system_emails.#{@system_email}.title") %></h2>
+
+<div class="small-12 column">
+  <div class="callout highlight">
+    <div class="row">
+      <div class="small-12 medium-4 column">
+        <strong><%= t("admin.newsletters.show.from") %></strong><br>
+        <%= Setting['mailer_from_address'] %>
+      </div>
+      <div class="small-12 medium-8 column">
+        <strong><%= t("admin.newsletters.show.subject") %></strong><br>
+        <%= @subject %>
+      </div>
+    </div>
+  </div>
+
+  <strong><%= t("admin.newsletters.show.body") %></strong>
+  <p class="help-text" id="phase-description-help-text">
+    <%= t("admin.newsletters.show.body_help_text") %>
+  </p>
+  <div class="newsletter-body-content">
+    <%= render file: "app/views/layouts/_mailer_header.html.erb" %>
+
+    <table cellpadding="0" cellspacing="0" border="0" style="background: #fff; margin: 0 auto; max-width: 700px; width:100%;">
+      <tbody>
+        <tr>
+          <%= render file: "app/views/mailer/#{@system_email}.html.erb" %>
+        </tr>
+      </tbody>
+    </table>
+
+    <%= render file: "app/views/layouts/_mailer_footer.html.erb" %>
+  </div>
+</div>