Add static site confirmation question and type to ProjectSetup

[schoenkaft]

• Adds a confirmation question type (was called 'boolean' before, but question type is more yes/no tailored).
• Adds a question to identify and configure static site setup, which will add a robots.txt file and activates the static site plugins (in theory it could install those ad-hoc, but out of scope for now).
• Refines the whole setup flow a bit:
  • The $answers variable is now concatenated instead of overwritten for each question round.
  • The assets installation/building is moved to the end (also helps when any Node installation issue arrises).
  • Proper URL validation.
• Added refined headings and prettier/colorized CLI output to distinguish between questions and defaults:

Refines and fixed #41.

[schoenkaft]

@HammenWS #30 is also adding some changes to the ProjectSetup class, would be great if we could test it all one final time when that setup/PR is finished.