Add packagegroup-core-buildessential

[Not heavily tested, but sent for discussion]

task-core-sdk is too big - for example, I simply don't want to ship tcl, ever =)
Historically distcc caused a large dependency graph explosion because it has
a utility which uses gtk+, although that was fixed.

packagegroup-core-sdk also includes coreutils, which is a bit
confusing; conceptually things dependent on coreutils should pull it
in explicitly, or possibly we just declare coreutils to be in the
minimal build set.

So packagegroup-core-buildessential is intended to be similar to
Debian's "build-essential" package.  It's the stuff needed by say 80+%
of components, not worth repeating over and over.

Signed-off-by: Colin Walters <walters@verbum.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>