* 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
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