Last changes to 2.0 versions

I'm going to release a finished 2.0 version with two last changes.

In version rc4 a new persistent variable was added to track the enabled pageears. That variable needs to be properly initialized when the module is updated from a previous version (no needed on install because that variable would have default value 0). In versions rc4 and rc5 I didn't do it so the process to upgrade the module to those versions required to disable the module to initialize that variable to 0. Now I coded an update_N hook that properly initializes that persistent variable so any previous versions can be upgraded with the normal process to upgrade a module. Just upload new files and run an update.php.

Since rc4 the module now uses two persistent variables, numEnabledPageears and current_pageear that are no more needed when the module is uninstalled so I added the proper code to delete those persistent variables on uninstall.

With those changes I think the module can be release as a finished 2.0 version and I will start the development to what would become a 2.1 version with new custom size feature.