Adopt SummerCMS v0.1.1 admin features

Datepickers on native time.Time / lagoon.Date fields, file uploads on
materials, readings and class sessions managed from the course form
(course_id made nullable).

models/deadlines/fields.yaml

@@ -6,10 +6,12 @@ fields:
         required: true
     due_at:
         label: jz.bm::lang.deadlines.due_at
-        type: text
+        type: datepicker
+        mode: datetime
+        format: d.m.Y H:i
+        firstDay: 1
         span: right
         required: true
-        comment: jz.bm::lang.common.datetime_comment
     kind:
         label: jz.bm::lang.deadlines.kind
         type: dropdown