fix: Pie charts should use column order, not "largest first"

Sorting by largest-first means that the column orders change with
every alternative.

Column-order still causes problems if you have different columns
in various alternatives, but at least in the case where
the columns are identical, the pie chart colors will be consistent.

src/charts/pie.vue

@@ -105,6 +105,7 @@ export default class VueComponent extends Vue {
   // format hover ?
   private data = [
     {
+      sort: false, // to keep colors consistent across plots
       labels: [] as any[],
       values: [] as any[],
       type: 'pie',