js/axis.js, js/scatterPlot: 6 labels on axis with nice_ceil() and nice_floor()

The labels on the grid (and the bar) view are now easier to read.
Moreover 6 = 5+1, and division by 5 is often nice.

Note that this wastes a limited amount of space.

browser/js/axis.js

@@ -36,7 +36,7 @@ function Axis (model, reverse) {
     this.reverse = reverse;
 }
 
-const NB_STEPS_IN_AXIS = 10; // Number (max) of labels per numerical axis
+const NB_STEPS_IN_AXIS = 6; // Number (max) of labels per numerical axis
 const NB_STEPS_BAR = 30; // Number (max) of labels per numerical axis in histograms
 
 Axis.prototype = {
@@ -188,6 +188,10 @@ Axis.prototype = {
                 min = 0;
                 max = 1;
             }
+            else {
+                min = nice_floor(min)
+                max = nice_ceil(max)
+            }
 
             if (has_undefined && ! use_log) {
                 min = min - (max - min)/NB_STEPS_IN_AXIS

browser/js/scatterPlot.js

@@ -841,7 +841,7 @@ ScatterPlot.prototype = {
      * compute the position of each rectangles / labels and start the display
      * */
     computeBarTab : function () {
-        var bar_max = this.computeBarMax();
+        var bar_max = nice_ceil(this.computeBarMax());
         var tab_length = Object.keys(this.barTab).length;
         var width = Math.min(0.08, 0.8 / tab_length);