Updated MenuBackend.h with default a value and bitwise hasChildren() ouput

- Allowed setting a default value (was value = 0)

- hasChildren() now returns useful information as to which direction the children are in the form of a 4-bit byte,
(B0001 = left, B0010 = up (before), B0100 = right, B1000 = down (after), B1111 = all... etc)