Timeline orientation / direction configuration

[mattbrehmer]

UI controls for configuring timeline orientation.

For linear timelines (currently earlier-to-recent corresponds to left-to-right): top-to-bottom, bottom-to-top, right-to-left (helpful for users whose written language is read right-to-left)

For radial timelines (currently earlier-to-recent proceeds clockwise): counter-clockwise

For spiral timelines (currently earlier-to recent proceeds outwards from center): inwards to center