DepositionGeant4: store G4Process->GetProcessSubType

The currently used GetprocessType() is only the process category (e.g. "Electromagnetic") but does not contain infos about the actual process taking place. The GetProcessName() currently employed reproduces the correct name at least, to also old data can still be correctly analyzed.

Example:

Type:     2
SubType:  2
TypeName: Electromagnetic
Name:     eIoni

Type:     2
SubType:  3
TypeName: Electromagnetic
Name:     eBrem

Type:     2
SubType:  12
TypeName: Electromagnetic
Name:     phot

This was uncovered in https://allpix-squared-forum.web.cern.ch/t/creation-process-name-vs-id-mismatch/598