Support optional and custom layers in hash URL

- extend layer control to get current active layers (and more)
- access layer control in hash instead of static initial list
- use ',' layer separator and encode layers individually, so that comma
in layer name gets encoded and is not mistaken as separator as with '-'

js/control/Control.Layers.js

@@ -0,0 +1,60 @@
+BR.ControlLayers = L.Control.Layers.extend({
+
+    getActiveLayers: function () {
+        var result = [];
+
+		for (var i = 0; i < this._layers.length; i++) {
+            var obj = this._layers[i];
+            if (this._map.hasLayer(obj.layer)) {
+                if (obj.overlay) {
+                    result.push(obj);
+                } else {
+                    result.unshift(obj);
+                }
+            }
+        }
+
+        return result;
+    },
+
+    removeActiveLayers: function () {
+        var removed = [];
+
+		for (var i = 0; i < this._layers.length; i++) {
+            var obj = this._layers[i];
+            if (this._map.hasLayer(obj.layer)) {
+                this._map.removeLayer(obj.layer);
+                removed.push(obj);
+            }
+        }
+
+        return removed;
+    },
+
+    getLayer: function (name) {
+        for (var i = 0; i < this._layers.length; i++) {
+			if (this._layers[i] && this._layers[i].name === name) {
+				return this._layers[i];
+			}
+		}
+    },
+
+    activateLayer: function (name) {
+        var obj = this.getLayer(name);
+        if (obj) {
+            this._map.addLayer(obj.layer);
+        }
+        return obj;
+    },
+
+    activateFirstLayer: function () {
+        for (var i = 0; i < this._layers.length; i++) {
+            var obj = this._layers[i];
+            if (!obj.overlay) {
+                this._map.addLayer(obj.layer);
+                break;
+            }
+        }
+    }
+
+});