Dynamic layers and lazy selection layer creation

With this change, the user provides a filter function instead of
an array of layers. Selection layers are created lazily, and
addition/removal of layers is not handled by the control to give
the user more options, as suggested by @elemoine.

src/objectliterals.jsdoc

@@ -205,7 +205,8 @@
  * @typedef {Object} ol.control.SelectOptions
  * @property {string|undefined} className CSS class name. Default is 'ol-select'.
  * @property {Element|undefined} element Element.
- * @property {Array.<ol.layer.Layer>} layers Layers to select features on.
+ * @property {undefined|function(ol.layer.Layer):boolean} layerFilter Filter
+ *     function to restrict selection to a subset of layers.
  * @property {ol.Map|undefined} map Map.
  * @property {Element|undefined} target Target.
  */