MuonR4 geometry - Move the chamber to be part of the ReadoutGeometry

In R4, the MuonChambers are created post-readout geometry by the MuonStationGeoHelpers and cached in a set. That has 2 caveats:

• The useage of them is quite cumbersome because one needs always to call the MuonChamberTool
• Non-standard grouping of readout elements to a chamber is not quite trivial

--> Move the chamber creation to the readout geometry creation and directly associate them with the readoutelement.

--> Delete the MuonStationGeoHelpers package

Tagging: @goblirsc, @damperia, @maharris, @pscholer, @ivyas, @smeriano