The production env seems to use a newer spack repo state → log4cxx is
newer than currently supported for BrainScaleS → quickfix: pin to old
version.

That's the first version that should really work :); rc1 experienced
scheduling problems when multiple users were accessing the same hardware
resource in parallel.

Add specs in spack.yaml. Update names for pyaescrypt and formencode and specify them as dependencies for tvb-framework.

`meta-brainscales` depends on `genpybind` which previously enforced
older versions of `llvm`.

This introduces some LLVM patches to enable code generation via
genpybind.

fixes to nest package according to @emueller changes in test_brainscales branch (revision required by @terhorst)