Object Requests & Simple Group Management Cmdlets

Very much refactoring.
Identified "group" requests as very important requests that handle groups, users, etc. Therefore they got own classes and some utility functions.

Implemented simple cmdlets for adding, getting and removing groups.
There are tests for both the requests itself and the cmdlets, inclusively the pipeline usage.

The way these cmdlets and requests are implemented and tested can be used as a reference when adding more cmdlets.
Major refactoring is hopefully done.

Edit 1:
Added new modifications that allow group querying. Didn't make sense to open a second merge request for this.