[XB] Core package 1.0

The package contains libraries we share between several our add-ons without this package our no addon will work however, having multiple add-ons to using the same files can sometimes cause a conflict between them, if they are using different versions of the files.

The package does not implement any visible functionality itself, it is just a collection of PHP classes reused by multiple add-ons. You don't need to install it if you are not using any of our add-ons.