EditMenu: let menu property be a component to lazy load it

Since all input fields have a menu assigned to it by
default (which in most cases never will be shown), it should
be an optimization to await creating it until needed.

Change-Id: I5777bbdae42103981e9b2f5ddfdfd763acea07ae
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>