Redo activity / installs chart in Plottable

![image](https://cloud.githubusercontent.com/assets/1400023/3742580/4ca26a84-176b-11e4-9741-c5cdf45bd843.png)
Features:
* Shows 7-day moving average rather than daily to give clearer view into trend
* Shows npm installations as a line chart, with a second axis
* Cleaner time axis
* Intelligent resize behavior
You can save a whole bunch of brackets:

```CoffeeScript
dataArr.slice(6).map (d, i) ->
  key: d[0]
  date: parseDate d[1]
  val: d[2]
  movingAvg: mAvg[i]
```