slide up current open message on opening another one instead of just fade out
visibly distinguish links
- 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
implement attachment download
adding mime icon to attachment list
fix layout of attachment download button and file type icon
fix download button
fix attachment layout
save-to-cloud implemented
capitalize Files to refer to ownCloud Files
save-to-cloud: add folder picker