Client side refactor, separating UI from data aggregation and feature computation

Okay, so there's still some rough corners... Especially in the UI, I took the liberty of addressing a few things while I was at it anyway. In this branch I have,
  * Written `telemetry.js` for reading histogram JSON data,
  * Rewritten `dashbaord.js` to reduce global variables and allow for multiple plot areas,
  * Fixed URL problem, with this hash strings are on the form: `#nightly/25/DNS_LOOKUP_TIME|nightly/25/A11Y_CONSUMERS/saved-session/Firefox`
   (We use pipe | to separate filter-path for multiple plot areas)...

As I said there are some rough corners, for instance I'm not sure the idea of creating `PlotArea` objects is brilliant...
Maybe we want a single plot with series from multiple measures... I'm not sure... Either way, UI and data aggregation is a at least separated.
So changing on either side should be easier now. Also `telemetry.js` offers quite a few features not yet exposed in the UI, standard deviation for instance, and ability to select a specific date range to aggregate the histogram over.