Copied the treemap from openspendingjs and added a new context property called drilldown (and can be overwritten in context).

This property is a function and gets called when a node is clicked. Default behaviour is the same behaviour as in openspendingjs' treemap.
Call the new treemap from oak11-13test
Removed redundant initialisations of the treemap for the dataset
Moved the javascript code to main javascript file (could be moved into specific file). Updated oak11-13test accordingly.
Modified the javascript to reload the site with url parameters that define where we've drilled until now. This creates a unique url for each drilldown.

Can be improved (e.g. the alert when no children are present or let user know where he/she is at without having to 'parse' it from the url parameters.

This introduces a dependency on purl.js (jQuery based url parser). It could be implemented easily but why go through the extra work?
Added breadcrumbs below the treemap (computed based on the url parameters and drilldowns)
Merge pull request #8 from tryggvib/gh-pages

Unique urls (via url parameters)