Hotfix/2389 scatter report not plotting

Initial fix for #2389 .

Hi @aronasorman .
I and @cpauya have some difficulties solving this issue it seems that the `exercise.json` change its format.
When the `search_fun_multi_path` return all items with a particular path it fails and raise an error `Unexpected error: list indices must be integers, not str`.
Do you have any idea on this?

I will attach my progress below it show the plot and some user.
![screen shot 2014-11-17 at 11 41 47 pm](https://cloud.githubusercontent.com/assets/4099119/5072334/b1f407a4-6eb3-11e4-9871-883e7f470e35.png)
.

In comparison of `central-develop`.
![screen shot 2014-11-18 at 12 17 29 am](https://cloud.githubusercontent.com/assets/4099119/5072871/a2a7463a-6eb8-11e4-9a36-6098ea8c4cdc.png)


Yeah I intentionally put `xaxis = "pct_mastery"` and ` yaxis = "effort"` so the drop down will default to this value.