Incoorporate feedback for verify activity

We got some feedback re https://mw-frontend-dev.tugraz.at/apps/signature/de/signature-verification

• Change https://www.signatur.rtr.at/de/vd/Pruefung to https://www.signaturpruefung.gv.at to be in line with the signature text and the other documentations
• Reference the possibility to verify the signature locally with Adobe Reader and link to https://security.tugraz.at/zertifikate/adobe/