Sample creation is broken

GUI:

1. create project
2. go to Sample view
3. create new sample or add from examples --> CRASH

changed milestone to %21 GUI fixes

added GUI crash release-critical labels

assigned to @j.wuttke

mentioned in issue #340 (closed)

added URGENT label

mentioned in merge request !1456 (merged)

mentioned in commit 69e5e0a2

closed with merge request !1456 (merged)