expose mobilize function for overriding

[scottjehl]

if any page that loads in could specify a custom mobilize function, it might make it easier to run custom scripts on certain pages.

[scottgonzalez]

Allow preventing the default initialization for pages by canceling the pagebeforecreate event. Closed by 5b2bbd7.

[scottgonzalez]

You can now run your own code before the standard page initialization by binding to the pagebeforecreate event or after the standard page initialization by binding to the pagecreate event. You can also prevent the standard page initialization by calling preventDefault() on the pagebeforecreate event.

We'll probably want to expose simple methods for handling parts of the standard page initialization so devs can leverage the existing code if they're preventing the default action.