* made several email related operations multi-account:
QueryEmailSnippets, QueryEmails, QueryEmailsWithSnippets
* add GetIdentitiesForAllAccounts
* add GetEmailsForAllAccounts
* jmap: add CreateIdentity, UpdateIdentity; groupware: add
GetIdentityById, AddIdentity, ModifyIdentity
* add temporary workaround until Calendars, Tasks, Contacts are
implemented in Stalwart when determining the default account for
those: use the mail one in the mean time
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