Erlang SPEC should have a separate subpackage for the GUI bits

[UnitedMarsupials-zz]

While I agree, that splitting into a multitude of small subpackages is not particularly useful -- while greatly increasing the SPEC-maintenance workload, one subpackage should be separate -- the one requiring the GUI bits (Tk and Wx-widgets).

Separating the GUI stuff out will make it much easier to install erlang on headless servers -- a no small thing with the rising popularity of server-software written in erlang (such as RabbitMQ).

I chose to call it "gui" (erlang-gui), but that does not matter. The changes are in "my": first, main change, and the minor correction.