add headless subpackage

[judovana]

This issue was pinpointed as regression in #848

Fedora/rehl packages contain headless subkg,m which is jre without graphiclal stack. The package is of nearly same size as would is current headfull package, but the depndencies are gone - about 1gb of dependencis (both manual and generated).
The headfull jre then requires headless jre and it isefl have just desktop integration and awt libraries.. and all the deps.
It is very cool feature, as we know, very widely known. There was request to have headless sdk subpkg, but we nwever made that step.

More detailed info in #848

@jiekang fyi!