Feature Request: Support for shared packages in external locations

[PMunkes]

Using aliBuild in a shared environment would currently require every software developer to provide a full copy of the whole sw/ folder. This means that in our use case it takes up 10GB of disk quota for packages that could be shared. --remote-store already saves the compilation time for these shared packages, but does not remove the disk space requirement.
Doing this would simply require setting symbolic links to the shared $PACKAGE_ROOT directories. If combined with atomic builds and a flag (--prefer shared) to always take non-dev-mode packages from the shared location, if possible, it would provide a safe and stable development environment.

[ktf]

Yes agreed. Supporting environment from modules as we do support brew on mac is one of the things which we would like to add, however it's a bit tricky because we need a sort of database of all the hashes for the packages in sw, so that we can do the matching with the local hashes.