Merge pull request #253 from jbraeuer/master

Berlin 2013: 1 gold sponsor.
DoDu 2013: adding Andrew Clay Shafer talk proposal 'There is no talent shortage'
DoDu 2013: hopefully fixing the bullet point list in Andrew's presentation
DoDu 2013: now hopefully fixing the link in Andrew's presentation
DoDu 2013: Oops that version of the presentation was not meant to be published
Update _sponsors.txt

Changed the ImmobilienScout24 sponsoring URL
Merge pull request #254 from IngmarKrusch/master

Berlin Sponsor update
Berlin 2013: Update program.