Refactor typescript merge master

Created by: bodograumann

I merged master into typescript-refactor to decrease the divergence between the two. Most changes went through automatically. I only had to manually resolve simple conflicts in README.md, docs/generators.md and modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java.

Cf. #802 (closed) CC @TiFu