fix for running standalone HCal

[mmlynari]

fix for running standalone HCal, otherwise, the code always looks for ECal

[kjvbrt]

What is the intended use of the m_useHalfTower variable?

Is it to ignore cells from the layers above 3? link

But the code will ignore all cells after first cell with layerID larger than 3 (including the current cell).

Also, 3 is a magic number. Better to have it as a configurable value.

[mmlynari]

my understanding was that this was an option that was used for some FCC-hh studies. I do not think we are currently using it. Maybe @faltovaj or @BrieucF can comment if this option can be of any use in the future or it can be removed

[BrieucF]

I'll merge and fix m_useHalfTower in another PR