Update perfect-scrollbar.js

Added onScroll, onPageResize, onUpdateBarSizeAndPosition events so the user can pass functions in to be run on these events, otherwise the plugin runs as normal. 
Also Added scrollTo function, so the user can tell the scroll bar to move to a specific position and if that position is available it will scroll to it and move the content. Only implemented x direction at this stage.

You can also give the plugin an ID, called containerId, to help you locate subcompenents of the plugin easier; if you don't the plugin will run as normal.

Also created scrollX & scrollY to persist scroll distances across the plugin (required in onScroll and onPageResize)
 
If a containerId is specified, the container and all associated subcontrols are prepended with that id (to make them easier to identify in the DOM when you're using multiple sets of perfect scroll on one page).