More control to multiple Y-Axes (Chartjs 2.0) (#367)

* More control to multiple y-axes definition

Author: anttimann

angular-chart.js

@@ -281,7 +281,7 @@
             data: item
           });
           if (yaxis) {
-            dataset.yAxisID = 'y-axis-' + (i + 1);
+            dataset.yAxisID = yaxis[i];
           }
           return dataset;
         })

examples/app.js

@@ -36,7 +36,7 @@
         console.log('No point');
       }
     };
-    $scope.multiAxis = true;
+    $scope.multiAxis = ['y-axis-1', 'y-axis-2'];
 
     $scope.options = {
       scales: {