Fix ol externs definitions

* Namespaces must be defined;
* Interfaces must be initialized.

externs/olx.js

@@ -594,6 +594,13 @@ olx.ViewOptions.prototype.zoom;
 olx.ViewOptions.prototype.zoomFactor;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.animation;
+
+
 /**
  * @typedef {{resolution: number,
  *     start: (number|undefined),
@@ -779,6 +786,13 @@ olx.animation.ZoomOptions.prototype.duration;
 olx.animation.ZoomOptions.prototype.easing;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.control;
+
+
 /**
  * @typedef {{className: (string|undefined),
  *     target: (Element|undefined)}}
@@ -1279,6 +1293,13 @@ olx.control.ZoomToExtentOptions.prototype.tipLabel;
 olx.control.ZoomToExtentOptions.prototype.extent;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.format;
+
+
 /**
  * @typedef {{dataProjection: (ol.proj.ProjectionLike|undefined),
  *     featureProjection: (ol.proj.ProjectionLike|undefined)}}
@@ -1742,6 +1763,13 @@ olx.format.WKTOptions;
 olx.format.WKTOptions.prototype.splitCollection;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.interaction;
+
+
 /**
  * Interactions for the map. Default is `true` for all options.
  * @typedef {{altShiftDragRotate: (boolean|undefined),
@@ -2307,6 +2335,13 @@ olx.interaction.SelectOptions.prototype.removeCondition;
 olx.interaction.SelectOptions.prototype.toggleCondition;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.layer;
+
+
 /**
  * @typedef {{brightness: (number|undefined),
  *     contrast: (number|undefined),
@@ -3097,6 +3132,13 @@ olx.FeatureOverlayOptions.prototype.map;
 olx.FeatureOverlayOptions.prototype.style;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.source;
+
+
 /**
  * @typedef {{culture: (string|undefined),
  *     key: string,
@@ -5241,6 +5283,13 @@ olx.source.ZoomifyOptions.prototype.tierSizeCalculation;
 olx.source.ZoomifyOptions.prototype.size;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.style;
+
+
 /**
  * @typedef {{fill: (ol.style.Fill|undefined),
  *     radius: number,
@@ -5662,6 +5711,13 @@ olx.style.StyleOptions.prototype.text;
 olx.style.StyleOptions.prototype.zIndex;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.tilegrid;
+
+
 /**
  * @typedef {{minZoom: (number|undefined),
  *     origin: (ol.Coordinate|undefined),
@@ -5847,6 +5903,13 @@ olx.tilegrid.ZoomifyOptions;
 olx.tilegrid.ZoomifyOptions.prototype.resolutions;
 
 
+/**
+ * Namespace.
+ * @type {Object}
+ */
+olx.View;
+
+
 /**
  * @typedef {{padding: !Array.<number>,
  *     constrainResolution: (boolean|undefined),