Missing backend features/connections for UI

• In MailListView.mailList, perform actual deletion of email when swiping right to left (.onDelete { })
• In ComposeModel, add functionality to @Published var encryptionOn. Currently it's just true. (This property affects and affected by encryption toggle button in ComposeViewHeader.)
• In FolderRowView, the folder.icon for all currently existing folders is identical. It seems that FolderRecord.icon returns the same Image for all folders. Probably needs to be addressed in FolderRecord.type?
• In FolderListView, folders are currently all in a single, lexicographically sorted array (via FolderRecord.FetchRequest). INBOX is therefore relatively far down. Should probably distinguish between a few hardcoded default folders that come first (Inbox, Drafts, Sent, Archive, Spam, Trash), and then list all user-created folders. Could be displayed separately via list Sections.
• Opening/reading an email does not change its isRead status. Currently it's unclear why a few mails in inbox are marked as read but most are not.
• MessageViewMain.deleteButton currently does not delete email
• When sending a Mail with attachments they are currently a) mentioned twice in the E-Mail body and b) either get sent twice or not at all