Add post and species forms

Squashed commit of the following:
Author: Hugo PRADIER <Hugo.PRADIER2@etu.uca.fr>
Author: bastien ollier <bastien.ollier@etu.uca.fr>
Author: clfreville2 <clement.freville2@etu.uca.fr>
Reviewed on #7

templates/post/edit.html.twig

@@ -0,0 +1,13 @@
+{% extends 'base.html.twig' %}
+
+{% block title %}Edit Post{% endblock %}
+
+{% block body %}
+    <h1>Edit Post</h1>
+
+    {{ include('post/_form.html.twig', {'button_label': 'Update'}) }}
+
+    <a href="{{ path('app_post_index') }}">back to list</a>
+
+    {{ include('post/_delete_form.html.twig') }}
+{% endblock %}