Show suggested monthly savings for a piggybank

If a piggybank has both a target date and a target amount, show how much money needs to be added to the piggybank each month to achieve both targets.

Strings are currently hard-coded because I want to gauge the reaction to this :)

resources/views/piggy-banks/show.twig

@@ -70,6 +70,14 @@
                                 {% endif %}
                             </td>
                         </tr>
+                        {% if piggyBank.targetdate %}
+                        <tr>
+                            <td>Suggested monthly amount to save</td>
+                            <td>
+                                {{ suggestedMonthlyAmount(piggyBank)|formatAmount }}
+                            </td>
+                        </tr>
+                        {% endif %}
                     </table>
                 </div>
             </div>