feat(timepicker): option to increment/decrement value on arrow click

I'm migrating from another timepicker and needed to do this to preserve the UX (using a length of 1, where paging with arrows feels very strange). I've kept the default behavior, but this commit makes it possible to add data-arrows="picker" to the element, which changes the arrow behavior so that the model is changed instead of the displayed range of values on arrow click.