remove unseen class for opened email to make it appear read, fix #18
Merge pull request #78 from owncloud/mark-as-read

remove unseen class for opened email to make it appear read, fix #18
better deletion feedback: make message which is about to be deleted transparent
- adding icons for download anf save to files
- show human file size
design improvements for attachments
adding id and mime to attachments

Conflicts:
	js/mail.js
	templates/index.php
different templates for single and multiple attachments
fixing wrong html
more design improvements for attachments, tweak button placement