1. Now that all the buildroots we need are open-source,
use defconfigs that ship with them instead of rolling our own.
2. New script: Packagaging/OpenDingux/build-all.sh
3. To avoid polluting top-level home directory, buildroot location
changed to `~/devilutionx-buildroot/$BUILDROOT_TARGET`.
4. Move OPK packaging script to its own file. This is to be able
to make a package for devilutionX in the buildroot itself.
Gleb Mazovetskiy