Remove includes of FEI4 from libYarr (needs checking)
A few things here:
- Add EventDataBase as base class of Fei4Data, only downside seems to be dynamic_cast in Fei4Histogrammer?
- Add registry of LoopScanBase
- Add writeNamedRegister so ScanFactory can change regs specified in json
- Add -MP to makefile so changing name of header file doesn't break the dependency checking
- Don't crash if FE doesn't have a channel set (something I ran into while exploring for strips code)