Changed logo image

- The original logo is white. Created black version for white background.
- Added logo in preview email and send email.

app/views/dashboard/mailer/forward.html.erb

@@ -59,5 +59,5 @@
       </tr>
     </tbody>
   </table>
-  <%= image_tag("decide_madrid.png", style: "max-width: 120px; display: block; margin: 0 auto; margin-top: 30px") %>
+  <%= image_tag("logo_header_black.png", style: "max-width: 120px; display: block; margin: 0 auto; margin-top: 30px") %>
 </td>

app/views/dashboard/mailing/index.html.erb

@@ -35,7 +35,7 @@
                    url: proposal_url(@proposal),
                    description: @proposal.summary } %>
 
-        <%= image_tag "decide_madrid.png" %>
+        <%= image_tag "logo_header_black.png" %>
       </div>
     </div>
   </div>