Identify inline mail attachments

Inline mail attachments should be identified and handled differently to other attachments.

At the moment inline content of mail attachments are directly appended to the mail content as well as being downloadable at the bottom of the mail screen. This makes the screen quite confusing as you end up duplicating the content. It would be much more useful if the inline attachment was highlighted.

Also inline attachments should not be searchable as an attachment as they are already searchable in mail.