Stackalytics widget is implemented

The widget shows summary on contribution for companies or modules. Options are
limited to project type, release and metric. Stats is shown as chart. Widget is
designed to be included into any web page, the data is loaded via jsonp.

Also:
* Options for project type, release and metrics are loaded in AJAX, not coded in template
* Moved code that handles drop-down selectors into stackalytics-ui.js

Change-Id: I3373ab1a627099f380070c0e3d90164ec0096039