Problem:
There are no buttons to move/copy a contact to another folder/adressbook ( or adding a contact to a group ).
Similar actions are offered in the mailview. This is a consistency problem.

Solution:
Buttons to move and copy contacts to another folder (address book)
P.ex. consistent with the already existing buttons to move/copy emails: a "more"-button at the upper right bar which opens a drop-down-menu with: -

• "copy contact" / "move contact" --> opens another drop-down-menu: to "folder name"
• "create a shortcut" --> opens another drop-down-menu: to "group name"

additionally (if possible): copy/move/cut contacts with cmd+C/V/X