Time axis

A better time axis. This is not ready yet, and still has a few bugs, but I'm making this PR so it's easier to get feedback.

Here are some pictures:
![screen shot 2014-07-16 at 6 36 34 pm](https://cloud.githubusercontent.com/assets/4107323/3607870/d07da292-0d52-11e4-98ff-7418e039281c.png)
![screen shot 2014-07-16 at 6 34 28 pm](https://cloud.githubusercontent.com/assets/4107323/3607871/d1b1a870-0d52-11e4-9418-576a00c8efb9.png)
![screen shot 2014-07-16 at 6 35 31 pm](https://cloud.githubusercontent.com/assets/4107323/3607872/d56649da-0d52-11e4-8684-ca58526c81d8.png)
![screen shot 2014-07-16 at 6 36 07 pm](https://cloud.githubusercontent.com/assets/4107323/3607873/d70e4166-0d52-11e4-9ff0-e29e26864a47.png)

Yes, I do kind of agree it should be in a separate file, but it ended up here because I originally thought the user may want to specify some custom intervals, so this array could be changed. However, it seems like a lot of burden for the user if they want to specify any reasonable minor/major interval pairing. 

Regardless, some people may want the option to specify intervals/formats.  One case I can think of is major week intervals, with minor days. Another may be that the data already spans one year, so it's not necessary to show year in the major intervals (though this could have something to do with formatters).

Anyways, I was thinking of redoing how to approach this. I think the current approach I have is very confusing, so I'm going to push up an alternate approach. However, I still think there's a better way to relate the minor to major interval relationship in one object rather than keeping two separate arrays.