AOSS -- Speakers corrections

Hey @oliviergoulet can we make the following changes to the Speakers section?

• remove Stefan Schumacher from the speakers list (remove him completely)

• change the picture of Ernst Stöckl Pukall with the one attached

• add Graham's photo, see attached

• add another speaker photo: Dr. Christian Mosch, Managing Director, Industrial Digital Twin Assocation (IDTA). see image attached