Add table column headers/remove empty lines from tables

Currently, the following pages contain tables with empty lines:

• doc.zih.tu-dresden.de/docs/archive/load_leveler.md
• doc.zih.tu-dresden.de/docs/archive/migrate_to_atlas.md
• doc.zih.tu-dresden.de/docs/archive/system_altix.md
• doc.zih.tu-dresden.de/docs/archive/vampirtrace.md
• doc.zih.tu-dresden.de/docs/software/perf_tools.md
• doc.zih.tu-dresden.de/docs/software/scs5_software.md