Detection and minimal support for RS 6.6 API

Detects and falls back to 6.0 API.
Workaround for buggy Invoke-RestMethod in PoSH v3.
Preliminary steps at implementing some RS 6.6 API changes
--DataQuery implemented via Invoke-RSDataQuery API
--Get-RSGroup can accommodate both RS 6.0 and RS 6.6 XML format