getFeatures method and featureInfo templates

To avoid surprises for application developers, this change
creates a new getFeatures method. So it is clear now beforehand
whether features or feature info markup is returned. The result
is now also grouped by layer, so application developers always
have a link between a layer and the feature info it returns.

To make getFeatureInfo return markup for vector layers, this
change also adds a featureInfoFunction property to the vector
layer, which gives developers full control over how features are
rendered to feature info markup.

src/ol/layer/vectorlayer.js

@@ -1,5 +1,6 @@
 goog.provide('ol.layer.Vector');
 
+goog.require('goog.array');
 goog.require('goog.asserts');
 goog.require('goog.events.EventType');
 goog.require('goog.object');
@@ -178,6 +179,13 @@ ol.layer.Vector = function(options) {
    */
   this.featureCache_ = new ol.layer.FeatureCache();
 
+  /**
+   * @type {function(Array.<ol.Feature>):string}
+   * @private
+   */
+  this.featureInfoFunction_ = goog.isDef(options.featureInfoFunction) ?
+      options.featureInfoFunction : ol.layer.Vector.uidFeatureInfoFunction;
+
   /**
    * TODO: this means we need to know dimension at construction
    * @type {ol.geom.SharedVertices}
@@ -378,6 +386,25 @@ ol.layer.Vector.prototype.parseFeatures = function(data, parser, projection) {
 };
 
 
+/**
+ * @return {function(Array.<ol.Feature>):string} Feature info function.
+ */
+ol.layer.Vector.prototype.getFeatureInfoFunction = function() {
+  return this.featureInfoFunction_;
+};
+
+
+/**
+ * @param {Array.<ol.Feature>} features Features.
+ * @return {string} Feature info.
+ */
+ol.layer.Vector.uidFeatureInfoFunction = function(features) {
+  var featureIds = goog.array.map(features,
+      function(feature) { return goog.getUid(feature); });
+  return featureIds.join(', ');
+};
+
+
 goog.require('ol.filter.Extent');
 goog.require('ol.filter.Geometry');
 goog.require('ol.filter.Logical');