Add speakers and sessions

from
- Dittmar
- Frederik
- Pascal
- Wolfram
Use dummy profile picture where img is missing
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.
Fixing issue #24

Added "this is a free event" information
Merge remote-tracking branch 'origin/iss24' into gh-pages