Add group_history to kernel.app on installation

If you don't add group_history to the modules section of kernel.app, and
subsequently make a release (using rebar, relx, whatever) that contains
the erts, it won't copy group_history to your new release.

kernel/group will then crash because it can't find group_history.
Merge pull request #9 from RJ/fix-kernel-app-file

Add group_history to kernel.app modules section on installation