Improve FocusNext and FocusPrevious

[sayanarijit]

As discussed in this thread we can improve the FocusNext and FocusPrevious behavior by making them loop, i.e. instead of stopping at the 0th or nth index, the focus can continue scrolling assuming (0 - 1 = n) and (n + 1 = 0) where n is the last index.

Other messages like *ByRelativeIndex will retain their original behavior.