MantleJS v0.1-alpha.3 for 1.20.1

Fixed bug:

• Cannot record pages added by custom transformers when closing a book. This causes that, when open the book next time, it cannot automatically turn to the last-opened page.

New feature:

• Allow directly create a PageDataJS via static methods createNew, createNewCustom and createEmpty.
  Java class PageDataJS still needs to be loaded manually using Java.loadClass().
  This is because pages creating via methods above needs more manual operations such as setting their parent.
  So PageDataJS is not provided directly by a global constant, to avoid confusing new developers.