RFE: apkg build-dep

Introduce new apkg build-dep command that will install (or list) package build dependencies/requirements for current (or selected) distro.

This should simply use existing distro commands such as apt-get builddep and yum build-dep to install/list requirements defined in respective package templates in distro/pkg/$DISTRO.

This will allow automatic preparation of machines/images for package builds with one command based on current information in project's distro/pkg/ and it's a necessary feature for fully automated packaging pipeline.