Refactor for py3 and recon-ng v5

[drtychai]

Slight changes made to script logic and layout, but the general concept is still followed.

Changes:

• recon-ng modules execute asynchronously
• recon-ng lib updated to support >=v5
• general refactor for readability
• Dockerfile added for improved portability

[drtychai]

Some areas we could improve upon before merging:

• Migrate altdns away from os.system
• Find a clean way to create/delete domain (input) file for altdns
• Additional recon-ng modules, if beneficial