Various improvements

[frankrousseau]

Problem

• More allowed extensions are needed: .kra, .sai, .sai2 (Krita and Paintool).
• Difficulty per task can't be set.
• Upcoming preferences are required: dark theme by default, publish by default for artists, and compression bitrates.
• It's not possible to mark all user notifications as read.
• More notifications are required: read/unread, watching/not watching.

Solution

• Add extensions to the allow list.
• Add a difficulty field (integer, 1 to 5) to the Task model.
• Add related preference field on the Organisation and Project models.
• Add migration file.
• Add a route to mark all notifications as read.
• Join subscription info to the notification query and add support for filtering on the read field and the fact there is a related subscription or not.

[EvanBldy]

Thanks