Support for Apples notes format

[konradrenner]

Apple notes are also synced via IMAP und thus notes are Mails (like Kolab stores notes), they also use html formatted mails for storing the notes, like Kolab does. For details look here: http://jpmens.net/2015/09/28/experiments-using-imap-for-notes/

A possibilty to support this would be to extend the sync and create a new account type.

This feature request is based on issue #149