Add speakers and sessions

from
- Dittmar
- Frederik
- Pascal
- Wolfram
Remove timestamps from the unscheduled talks.
Add "GDG" ribbons to the speakers.
Add grandcentrix-ribbon-border-color to scss
Add Dittmars profile picture.
Add Pascals profile picture.
Contact email address info@gdg-dus.de.
Contact email address info@gdg-dus.de.
Add Georg Zweschper.
Add Denis and Brian
Add Nabil Ben Said
Fix Social link from Denis and Frederik.
Merge branch 'gh-pages' into develop
Schedule "coming soon".
Prominent "Register"