Contact: Add method for snippet chooser search

Add method chooser_search to the model which can be used by the
snippet chooser. This method does a case blind "contains"-search
agains "first_name last_name".

mpicms/personal/models.py

@@ -1,6 +1,8 @@
 from django.db import models
 from django.utils.translation import gettext_lazy as _
 from django.core.validators import MaxValueValidator
+from django.db.models import CharField, Value as V
+from django.db.models.functions import Concat
 
 from wagtail.core.models import Orderable
 from wagtail.admin.edit_handlers import FieldPanel, MultiFieldPanel, InlinePanel
@@ -146,6 +148,8 @@ def __str__(self):
         else:
             return self.email
 
+    def chooser_search(query):
+        return Contact.objects.annotate(display_name=Concat("first_name", V(" "), "last_name")).filter(display_name__icontains=query)
 
     class Meta:  # noqa
         verbose_name = 'Contact'