Series override option to hide legend entries

Adds a series override option to hide certain series from the legend.

* public/app/components/timeSeries.js: boolean flag to decide display in
  legend and application of override option for this flag
* public/app/panels/graph/legend.js: exclude hidden series
* public/app/panels/graph/seriesOverridesCtrl.js: add legend override
  option

This fixes #2324

public/app/components/timeSeries.js

@@ -13,6 +13,7 @@ function (_, kbn) {
     this.color = opts.color;
     this.valueFormater = kbn.valueFormats.none;
     this.stats = {};
+    this.legend = true;
   }
 
   function matchSeriesOverride(aliasOrRegex, seriesAlias) {
@@ -55,6 +56,7 @@ function (_, kbn) {
       if (override.fillBelowTo !== void 0) { this.fillBelowTo = override.fillBelowTo; }
       if (override.color !== void 0) { this.color = override.color; }
       if (override.transform !== void 0) { this.transform = override.transform; }
+      if (override.legend !== void 0) { this.legend = override.legend; }
 
       if (override.yaxis !== void 0) {
         this.yaxis = override.yaxis;

public/app/panels/graph/legend.js

@@ -130,6 +130,10 @@ function (angular, app, _, kbn, $) {
             if (panel.legend.hideEmpty && series.allIsNull) {
               continue;
             }
+            // ignore series excluded via override
+            if (!series.legend) {
+              continue;
+            }
 
             var html = '<div class="graph-legend-series';
             if (series.yaxis === 2) { html += ' pull-right'; }

public/app/panels/graph/seriesOverridesCtrl.js

@@ -104,6 +104,7 @@ define([
     $scope.addOverrideOption('Y-axis', 'yaxis', [1, 2]);
     $scope.addOverrideOption('Z-index', 'zindex', [-1,-2,-3,0,1,2,3]);
     $scope.addOverrideOption('Transform', 'transform', ['negative-Y']);
+    $scope.addOverrideOption('Legend', 'legend', [true, false]);
     $scope.updateCurrentOverrides();
 
   });