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/reading.go

@@ -11,7 +11,7 @@ import (
 // Reading is one lektura on a course's reading list.
 type Reading struct {
 	ID         uint      `gorm:"column:id;primaryKey"`
-	CourseID   uint      `gorm:"column:course_id"`
+	CourseID   *uint     `gorm:"column:course_id"`
 	Course     *Course   `gorm:"foreignKey:CourseID"`
 	Title      string    `gorm:"column:title"`
 	Author     *string   `gorm:"column:author"`