Feature: IP Scanner detect common ports

[BornToBeRoot]

Please provide some details about this pull request:

• Improve host detection by scanning for common ports
• Rewrite ThreadPool handling in applicaton
• Some code cleanup / refactoring / improvements
• Port Scanner fix lookup if service/description is empty

Fixes #245

ToDo:

• Hide port column if port scan is disabled
• Export ports / port state
• Update documentation to reflect this changes

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