Date scale

[heckj]

Add the pieces to enable an explicit calendaring scale - over Date.

The ticks and nice values, in particular, will be specific to dates. Instead of working from the underlying "seconds since..." as a number, it should correlate to a range based on calendrical values (seconds, minutes, hours, days, weeks, months, years) - and then generate both niceVersions of these values as well as steps and increments with those ranges that use "nice" increments (1, 2, 5, or 10)