Upload Custom Thumbnail for a Lecture

[feriel97]

Motivation and Context

resolves #1155

Description

Currently the thumbnail for the videos is generated automatically. The new Upload Custom Thumbnail button allows the admin users to be able to drag and drop an image file as a custom thumbnail for a lecture. The UI is still a work in progress and the file upload without drag and drop will be supported for better support on other devices such as mobiles.

The current to-dos:

• [x] Visual Feedback for the upload to the user
• [x] Preview the thumbnail

Optional:

• Option to go back to the automatically generated thumbnail

Steps for Testing

Prerequisites:

• 1 Lecturer
• 1 Lecture
• 1 Picture

1. Log in
2. Navigate to the Admin Panel
3. Select a Course
4. Select a Lecture
5. Edit Lecture
6. Toggle the button
7. Drag and drop the file
8. Select Save Lecture

Screenshots

[kordianbruck]

@joschahenningsen ping please re-review?