Time Axis and Formatter

Reopening #562 now that #564 has been merged in. 

I've removed the Time Scale changes for now because they weren't playing nice with the domainers #553  (since the domainer assumes that they are quantitive scale). 

For the Time formatter, I wasn't too sure what to do with precision. Currently I'm ignoring it, but we may want to make it do something in the future. 
Consider taking a look at the text-translation code used in `Numeric` Axis. You should be able to position `<text>` elements using the `x` and `y` attributes, rather than transforms.