rationalize LArCellHVCorrAlg
The component called 'LArCellHVCorrAlg' is actually a AlgTool.
- (Dramatically) simplify the code, deriving from ICaloCellMaker instead of CaloCellCorrection to pull the ReadCondHandle de'refing out of the loop over cells.
- Rename to LArCellContHVCorrTool since it's a Tool acting on an entire cell container
Tagging @ssnyder and @pavol who recently worked on this code.