Add changes needed to compile packages on JURECA@JSC

Changes:

• hxtorch and pynn-brainscales now also link against implicit dependencies
• Fixed paths on JURECA
• Set correct dependencies on JURECA
• Removed some external packages on JURECA as they were not fully working with spack (e.g. due to missing executables)

mentioned in commit 9c9bed04

merged

mentioned in issue #40 (closed)

mentioned in issue #52 (closed)