Consistent use of translation keys to fix divergences between PDF and HTML visualization

The following discussion from !55 (merged) should be addressed:

• @barbara.dewein started a discussion:

  solution for html and pdf divergences needed: e.g. html has differnt keys for "base amount" and "net" whereas pdf has only one key

consistent use of "Gesamtsumme (netto)" and "Gesamtsumme (brutto)"

continue with section "Details" on 5.7.22