Update from prototype

[thet]

• Update Prototype to fix a problem with some previews not shown in help pages.
  Note: This uses the submodule "_includes/patterns" branch "reverse-sentinel" from Reverse the sentinel inclusion logic Patternslib/patterns-includes#3

• Fix towncrier config.

Ref: scrum-3430

NOTE: Until the problem addressed by Patternslib/patterns-includes#3 is fixed, we need to use this branch from that PR. Of course, we can always rebase the branch with current patterns-includes master.

Ref:

• Scrum ticket: https://github.com/syslabcom/scrum/issues/3430
• Issue: https://github.com/syslabcom/oira.prototype/issues/559
• Fix: Reverse the sentinel inclusion logic Patternslib/patterns-includes#3
• Inclusion of the fix in oira.prototype, probably obsolete or at least needs to be updated to the correct git submodule commit hash: https://github.com/syslabcom/oira.prototype/pull/557