rest: Add RemoveHeader and SetCookie method
rest: Add RemoveHeader and SetCookie method

These methods extend the rest package to support the cookie header and
header deletion.

The deletion is necessary to delete an existing authorization header if
cookie auth should be used.

ncw/rclone,seuffert/rclone,yonjah/rclone,B4dM4n/rclone,yonjah/rclone,seuffert/rclone,yonjah/rclone,seuffert/rclone,olihey/rclone,olihey/rclone,ncw/rclone,ncw/rclone,olihey/rclone,B4dM4n/rclone,seuffert/rclone,yonjah/rclone,ncw/rclone,B4dM4n/rclone,B4dM4n/rclone,olihey/rclone