Codesigndoc - better debug/error logging

codesigndoc now prints the Xcode output if xcodebuild -list (scheme listing) fails

Fix PR: Include and print the xcodebuild output if scheme scan fails by viktorbenei · Pull Request #34 · bitrise-io/codesigndoc · GitHub

Additionally it now prints the Xcode version before running the first xcodebuild command

Deployed in v0.9.18