* add URL to retrieve all the mailboxes for all the accounts of a user,
as a first use-case for an all-accounts operation, as
/accounts/all/mailboxes
* add URL to retrieve mailbox changes for all the mailboxes of all the
accounts of a user, as a first use-case for an all-accounts
operation, as /accounts/all/mailboxes/changes
* change the defaultAccountId from '*' to '_', as '*' rather indicates
"all" than "default", and we might want to use that for "all
accounts" operations in the future
* refactor(groupware): remove the accountId parameter from the logger()
function, as it is not used anyways, but also confusing for
operations that support multiple account ids
* 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
