Colours in cost centre view should match colours in the other charts

[mpickering]

At one point in time, the colours in the cost centre view matched up with the colours in the main chart. In more recent times, I changed the colour ordering of the main charts to be ordered by the k value, but didn't update the cost centre chart to reflect this new colour ordering.

I tried to do this quickly but applying the colour scheme in vega is a bit more complicated than in vega-lite. In particular, if you try modifying Eventlog/Trie.hs to include the band identifier (the first component of the triple) then it is included in the vega output as an integer and hence is a continuous scale. Therefore the ordinal scales don't work and you need to transform the data first before

1. Modify Eventlog/Trie.hs to include the band identifier in the cost centre data output.
2. Modify javascript/ccmap.vg to apply the colour scheme correctly.

A good way to experiment here is to render the chart and then click on the dropdown in the top-right and open the cost centre chart in the vega editor. Then you can quickly play around with the different scale options with a live visualisation.