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/class_sessions/fields.yaml

@@ -13,16 +13,20 @@ fields:
         emptyOption: jz.bm::lang.common.none
     starts_at:
         label: jz.bm::lang.sessions.starts_at
-        type: text
+        type: datepicker
+        mode: datetime
+        format: d.m.Y H:i
+        firstDay: 1
         span: left
         required: true
-        comment: jz.bm::lang.common.datetime_comment
     ends_at:
         label: jz.bm::lang.sessions.ends_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
     room:
         label: jz.bm::lang.sessions.room
         type: text