Add a hidden XandYAxis enum value

For Qt 5 XandYAxis is being renamed to XAndYAxis to more consistently
follow capitalization rules. Add an undocumented XandYAxis variable to
ease porting.

Change-Id: Id9e41dd5578373f5f557937da889a9326ff12e53
Reviewed-by: Martin Jones <martin.jones@jollamobile.com>