proper d3 chart

[danse]

wrap the charting part in a proper d3 chart with auto scaling axes

[danse]

this chart should adapt in a flexible when the countries change, to allow selecting a country

[danse]

the chart should support also transitions on one dimension. the conversion and the data structure is made in a way that every point may have several indicators associated with it, so the chart should be ready to show the transition between different indicators. see also #8