So I could see all my contacts together and send email by just a click
It is not possible at the moment but we will consider it and maybe will implement it in the future.
Actually it already was implemented in version 4 as I can see here http://actualdownload.com/pictures/sc…
The other obvious option would be changing the action of double clicking on a contact in contacts section to send email instead of edit contact.
But I think contacts on the sidebar would be nicer.
Yes it was, but we decided to remove it as part of the design changes.