Add getter methods for original and action to the Page object.

[Hydraner]

First of all, I am pretty new to grav and I'm pretty exited working with it. I come from the Drupal world and I love Grav because it's so similar it its concepts but still lightweight and way better to work with for smaller sites.

So pls give me a hint if I don't do this right here, it's my first contribution!

I started building a Plugin for automatic redirects when changing the folder's name in order to keep SEO ranking. To do that, I need to compare the original version with the current one when Saving a Page. Additionally I found it useful to check for the move action at this point, this way I don't need to compare the objects to see if something changes.

However, the _original property is private and cannot be accessed onAdminSave event.