This will ease portal templates configuration.

This was introduced by mistake in bddd1eb6

Allow to just request default profile. Set usual site id and by default lock
down backend access.

Also use directly parameters instead of json.

Json would require in-code parsing, which would lead to complex recipes.

It will request all required services. json is in parameter dict.

More: software.cfg does not have to specify a lot of parts, as main template
is driving the choice process.

Keys are becoming lowercased.

Some more is required on filesystem level which shall result in generating
correct zope structure.

Thanks to this instantiation is more self documented.