d3 add precip cells for one timestep

[lindsayplatt]

You can still hover over counties below the precip cells. Not sure if this is weird behavior or not, but I can easily turn it off by setting "pointer-events". Only doing one timestep right now. Animations through time is the next hurdle :)

This requires vizlab v0.2.2.9008 a la USGS-VIZLAB/vizlab#326

[lindsayplatt]

I did notice that adding those precip cells make this noticeably slower, so we will definitely need to discuss where to draw the line between R and D3.

[aappling-usgs]

What becomes slower - the page load, the interaction after loading, or both?

[lindsayplatt]

I think it's the loading? You can see the map popup with everything, but there is a lag for when your mouse interactions start.

[jordansread]

but once that is up and running, no drag or lag in the mouseovers?

[lindsayplatt]

There's a little bit of a lag when you first try, then it looks slightly lagged when you go super super fast

[lindsayplatt]

Thanks to some help from @mwernimont, css is now working and implemented. When this PR is merged, it will fix #38

[aappling-usgs]

I bet we can improve the load time by packaging the data more concisely. After the polygons are all in place, I'm skeptical that D3 vs R have much control - we might even need to move away from SVG if we need still more speed. Overall, feeling optimistic about D3 and looking forward to experimenting for performance.

[lindsayplatt]

@aappling-usgs I'm interested in getting some more hands on this branch to play around with how the data is formatted and passed through the process. I'm going to merge this for now, so we can keep moving along before Tech Tues.