* refactor some pkg/jmap and groupware methods to make more sense from
an API point-of-view
* add path parameter documentation, but automate it by injecting their
definition into the OpenAPI YAML tree that is extracted from the
source code using go-swagger as it is too cumbersome, repetitive and
error-prine to document them in the source code; wrote a TypeScript
file apidoc-process.ts to do so
* add generating an offline HTML file for the OpenAPI documentation
using redocly, and injecting a favicon into the resulting HTML; wrote
a TypeScript file apidoc-postprocess-html.ts to do so
* add more documentation for properties
* fixes after a bit of trial-and-error with go-swagger
* fix email filter marshalling when there are no search criteria
* introduce an apidoc.yml that contains Swagger data and is merged when
generating the swagger.yml from sources
