Fix issue templates

[dennisvang]

• fixes duplicate ids in feature-request template

• enables blank issues:
  Although issue templates are useful when used properly, I see several drawbacks:

  • increased threshold for reporting issues (reporter's time is valuable!)
  • increased maintenance burden (current PR is template maintenance...)
  • often too restrictive or not a good fit
  • often too verbose

  By enabling blank issues, reporter gets to choose.