Fixing issue #23

Added initial impressum page.
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 #23

Changed impressum email address to info@gdg-dus.de
Changed organizer email
Merge remote-tracking branch 'origin/iss23' into gh-pages
Fixing issue #24

Added "this is a free event" information
Merge remote-tracking branch 'origin/iss24' into gh-pages
Revert "Revert "Fixing issue #24""

This reverts commit 2f71f6d262b6b7c8908aa52225431ef475973203.

Revert "Fixing issue #24"

This reverts commit
84eb9c778ff08a4eb723ad4868624f84ce3cb619.
Fixing issue #24

Again previously I started from wrong branch
Fixing issue #24

Enabled tickets.html block
Team page update
Added grandcentrix to partners
added gcx icon
Update _config.yml