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).

controllers/courses/config_relation.yaml

@@ -0,0 +1,46 @@
+# Readings and class sessions are created, edited and deleted from the
+# course form, also before the course is first saved (course_id is
+# nullable). There is no link or unlink: a row without a course is only
+# ever one pending on an unsaved form.
+readings:
+    label: jz.bm::lang.courses.readings
+    view:
+        list:
+            columns:
+                title:
+                    label: jz.bm::lang.common.title
+                    searchable: true
+                author:
+                    label: jz.bm::lang.readings.author
+                is_required:
+                    label: jz.bm::lang.readings.is_required
+                sort_order:
+                    label: jz.bm::lang.common.sort_order
+        toolbarButtons: create|update|delete
+        showSearch: true
+    manage:
+        form: ~/plugins/jz/bm/models/readings/fields_course.yaml
+        list:
+            columns:
+                title:
+                    label: jz.bm::lang.common.title
+sessions:
+    label: jz.bm::lang.courses.sessions
+    view:
+        list:
+            columns:
+                starts_at:
+                    label: jz.bm::lang.sessions.starts_at
+                ends_at:
+                    label: jz.bm::lang.sessions.ends_at
+                room:
+                    label: jz.bm::lang.sessions.room
+                kind:
+                    label: jz.bm::lang.sessions.kind
+        toolbarButtons: create|update|delete
+    manage:
+        form: ~/plugins/jz/bm/models/class_sessions/fields_course.yaml
+        list:
+            columns:
+                starts_at:
+                    label: jz.bm::lang.sessions.starts_at