Add username in autocomplete field for members

coin/members/autocomplete_light_registry.py

@@ -8,7 +8,8 @@ from models import Member
 autocomplete_light.register(Member,
                             # Just like in ModelAdmin.search_fields
                             search_fields=[
-                                '^first_name', 'last_name', 'organization_name'],
+                                '^first_name', 'last_name', 'organization_name',
+                                'username'],
                             # This will actually data-minimum-characters which
                             # will set widget.autocomplete.minimumCharacters.
                             autocomplete_js_attributes={