improvements and fixes

[achimmihca]

Thank you for this project! I used it successfully together with this Java SP library: https://github.com/onelogin/java-saml

However, I had to adjust some minor stuff and I want to share my findings:

• added vscode launch config
  • therefor, moved file in bin-folder one level up and renamed it to "run-mock-idp.py" (see also #4 )
• set logout_url in default_config.yaml to fix exception and make it clear that this config exists
  • there was a crash in response.py in create_logout_response because 'logout_url' was not a valid key
• use sha256 for signature and digest. sha1 is deprecated and may cause issues
  • the Java SP library was complaining because of sha1
• set IssueInstant in UTC form of ISO-8601 format
  • the Java SP library was complaining because of this
• use localhost (127.0.0.1) as default host address
  • not sure why anyone would want 0.0.0.0. I never saw this. with 127.0.0.1 it is usable out-of-the-box