installability: Print missing dependencies

List the missing packages and the packages they break. This provides a quickly actionable data point, since it gives an indication of what needs to be added and how many packages it would fix.

added 6 commits

• 06b40b48...9ab8d8f6 - 5 commits from branch apertis/v2021dev1
• 1b5d1a10 - installability: Print missing dependencies

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merged