Update core/model/modx/mail/modmail.class.php

Added image embedding. I think it would be usefull when there is no ability to insert images with absolute urls into message body.
Update core/model/modx/mail/modphpmailer.class.php

Added image embedding. I think it would be usefull when there is no ability to insert images with absolute urls into message body.
Merge remote-tracking branches 'dryamvlad/patch-2' and 'dryamvlad/patch-3' into mail-image-embed

* dryamvlad/patch-2:
  Update core/model/modx/mail/modmail.class.php

* dryamvlad/patch-3:
  Update core/model/modx/mail/modphpmailer.class.php
add changelog
[#10146] Add embedded image support to modMail

Merge branch 'mail-image-embed' into develop

* mail-image-embed:
  add changelog
  Update core/model/modx/mail/modphpmailer.class.php
  Update core/model/modx/mail/modmail.class.php