Decide on usage of package extensions in GAP 4.13

[schnellecom]

Some functionality e.g. Isomorphism tests are dependent on other packages. Therefore we could transition to marking these packages as extensions and only having the functionality if the package is installed.
However, since this is a GAP 4.13. functionality we would need to decide to either make this the minimum required version or to not have the functionalities in old GAP versions.