Added axis label

src/Stats/Charts/CellsChart.js

@@ -5,6 +5,7 @@ const ChartController = require("./ChartController");
 class CellsChart extends ChartController {
     constructor() {
         super("Organism Size / Composition", 
+            "Avg. Number of Cells per Organism",
             "Note: to maintain efficiency, species with very small populations are discarded when collecting cell statistics.");
     }