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/_delete_form.html.twig

@@ -0,0 +1,4 @@
+<form method="post" action="{{ path('app_post_delete', {'id': post.id}) }}" onsubmit="return confirm('Are you sure you want to delete this item?');">
+    <input type="hidden" name="_token" value="{{ csrf_token('delete' ~ post.id) }}">
+    <button class="btn">Delete</button>
+</form>