Statement query changes

clarified that the multipart attachment format is to be used in responses when attachments are requested even if there are no attachments.
simplified existing query options while expanding them. (see extensive changes)
group filter updates, activity & group equality tweaks
targeted statement search clarificaton
Moved single-statement queries in to the main query parameter block in order to allow "attachments" and "format" to apply
added "voidedStatementId" to allow fetching voided statements
added "viewId" to allow limiting statement results on any pre-defined views the LRS provides