personal: Use index.AutocompleteField

Wagtail is changing its search API [1]. There is a documentation PR pending at [2].

Our automplete hack - patch to make Wagtail Snippet Chooser use
.autocomplete() instead of .search() - stopped working after the Wagtail
update for the Contact snippet. Use wagtail.search.index.AutocompleteField
in Contact model to specify, which fields should be indexed for autocompletion.

[1] https://github.com/wagtail/wagtail/issues/4937
[2] https://github.com/wagtail/wagtail/issues/4938

mpicms/personal/models.py

@@ -126,8 +126,11 @@ class Contact(index.Indexed, ClusterableModel):
 
     search_fields = [
         index.SearchField('first_name', partial_match=True),
+        index.AutocompleteField('first_name'),
         index.SearchField('last_name', partial_match=True),
+        index.AutocompleteField('last_name'),
         index.SearchField('email', partial_match=True),
+        index.AutocompleteField('email'),
         index.SearchField('phone'),
         index.SearchField('room'),
         index.FilterField('is_active')