[#83,facets][s]: add date histogram facet support.

* Incomplete in various ways (e.g. cannot apply filter correctly using it) but can add and view.

src/model.js

@@ -297,6 +297,17 @@ my.Query = Backbone.Model.extend({
     };
     this.set({facets: facets}, {silent: true});
     this.trigger('facet:add', this);
+  },
+  addHistogramFacet: function(fieldId) {
+    var facets = this.get('facets');
+    facets[fieldId] = {
+      date_histogram: {
+        field: fieldId,
+        interval: 'day'
+      }
+    };
+    this.set({facets: facets}, {silent: true});
+    this.trigger('facet:add', this);
   }
 });
 

src/view-grid.js

@@ -71,6 +71,9 @@ my.DataGrid = Backbone.View.extend({
       facet: function() { 
         self.model.queryState.addFacet(self.state.currentColumn);
       },
+      facet_histogram: function() {
+        self.model.queryState.addHistogramFacet(self.state.currentColumn);
+      },
       filter: function() {
         self.model.queryState.addTermFilter(self.state.currentColumn, '');
       },
@@ -164,7 +167,8 @@ my.DataGrid = Backbone.View.extend({
               <div class="btn-group column-header-menu"> \
                 <a class="btn dropdown-toggle" data-toggle="dropdown"><i class="icon-cog"></i><span class="caret"></span></a> \
                 <ul class="dropdown-menu data-table-menu pull-right"> \
-                  <li><a data-action="facet" href="JavaScript:void(0);">Facet on this Field</a></li> \
+                  <li><a data-action="facet" href="JavaScript:void(0);">Term Facet</a></li> \
+                  <li><a data-action="facet_histogram" href="JavaScript:void(0);">Date Histogram Facet</a></li> \
                   <li><a data-action="filter" href="JavaScript:void(0);">Text Filter</a></li> \
                   <li class="divider"></li> \
                   <li><a data-action="sortAsc" href="JavaScript:void(0);">Sort ascending</a></li> \

src/view.js

@@ -399,6 +399,9 @@ my.FacetViewer = Backbone.View.extend({
         {{#terms}} \
           <li><a class="facet-choice js-facet-filter" data-value="{{term}}">{{term}} ({{count}})</a></li> \
         {{/terms}} \
+        {{#entries}} \
+          <li><a class="facet-choice js-facet-filter" data-value="{{time}}">{{term}} ({{count}})</a></li> \
+        {{/entries}} \
         </ul> \
       </div> \
       {{/facets}} \
@@ -421,6 +424,15 @@ my.FacetViewer = Backbone.View.extend({
       facets: this.model.facets.toJSON(),
       fields: this.model.fields.toJSON()
     };
+    tmplData.facets = _.map(tmplData.facets, function(facet) {
+      if (facet._type === 'date_histogram') {
+        facet.entries = _.map(facet.entries, function(entry) {
+          entry.term = new Date(entry.time).toDateString();
+          return entry;
+        });
+      }
+      return facet;
+    });
     var templated = $.mustache(this.template, tmplData);
     this.el.html(templated);
     // are there actually any facets to show?