Dependency check of the tidy tool should verify the license

[gnzlbg]

Currently, in the dependency-check of the tidy tool, dependencies having an incompatible license are white-listed, and the actual license is documented in a comment.

Instead, the actual license should be documented in code, and the tool should check that the license is actually correct. When updating dependencies, the license might silently change into an incompatible one, and right now we don't detect this.