Make selection scroll optional

It's not essential but rather causes several problems.

README.md

@@ -312,6 +312,10 @@ The number of pixels the content height can surpass the container height without
 When set to false, when clicking on a rail, the click event will be allowed to propagate.  
 **Default: true**
 
+### useSelectionScroll
+When set to true, you can scroll the container by selecting text and move the cursor.  
+**Default: false**
+
 ## Events
 
 perfect-scrollbar dispatches custom events.

examples/text-content.html

@@ -32,7 +32,9 @@
     <script>
       var $ = document.querySelector.bind(document);
       window.onload = function () {
-        Ps.initialize($('#description'));
+        Ps.initialize($('#description'), {
+          useSelectionScroll: true
+        });
       };
       $('#redraw').addEventListener('click', function () {
         var oldHtml = $('#description').innerHTML;

src/js/plugin/default-setting.js

@@ -4,16 +4,17 @@
 'use strict';
 
 module.exports = {
-  wheelSpeed: 1,
-  wheelPropagation: false,
-  swipePropagation: true,
-  minScrollbarLength: null,
   maxScrollbarLength: null,
-  useBothWheelAxes: false,
+  minScrollbarLength: null,
-  useKeyboard: true,
-  suppressScrollX: false,
-  suppressScrollY: false,
   scrollXMarginOffset: 0,
   scrollYMarginOffset: 0,
-  stopPropagationOnClick: true
+  stopPropagationOnClick: true,
+  suppressScrollX: false,
+  suppressScrollY: false,
+  swipePropagation: true,
+  useBothWheelAxes: false,
+  useKeyboard: true,
+  useSelectionScroll: false,
+  wheelPropagation: false,
+  wheelSpeed: 1
 };

src/js/plugin/initialize.js

@@ -31,7 +31,10 @@ module.exports = function (element, userSettings) {
   dragScrollbarHandler(element);
   mouseWheelHandler(element);
   nativeScrollHandler(element);
+
+  if (i.settings.useSelectionScroll) {
     selectionHandler(element);
+  }
 
   if (h.env.supportsTouch || h.env.supportsIePointer) {
     touchHandler(element, h.env.supportsTouch, h.env.supportsIePointer);