MuonStationGeoHelpers - Simplify coordinate systems & test

• Synchronize the MuonChamber coordinate system with the one used in the Acts::Volume:

local axis	Description
x	Parallel with the tube wires / chamber edge (Distinguish long & short width)
y	In chamer plane orthogonal to tube wires - increasing tube number --> negative y
z	Points to the cavern walls

• Pull the TransformCache into the MuonChamber --> StationCenter cache has been obsoleted
• Introduce highVolt position into the MdtReadoutElement
• Introduce leftStripEdge & rightStripEdge position into the RpcReadoutElement
• Add generic readoutElement getter to the MuonDetectorManager
• Build chambers from Tgc detectors --> Thus far same granularity as the corresponding readout elements. Need to investigate whether the Tgc chambers can be absorbed into the close-by Mdt middle stations

Tagging: @maharris, @damperia, @goblirsc