Fix for photonIdMva systematics which was not working with the `doDiPhoMvaUpFront` flag.

- Added dedicated single photon smearer.
- Added array to cache photon id mva in LoopAll.
- This also properly accounts for changes in preselection efficiency.
- Cached values are already shifted by systematic uncertainty.
- FIXME: if doDiPhoMvaUpFront is not active, the old method is used.
- FIXME: need to move photon ID corrections inside the smeaer (ok for now since there are none).
- Also removed unused MvaAnalysis class and hard-coded photonIdMva systematics
Merge pull request #253 from musella/fix_idmva_systs

Fix for photonIdMva systematics which was not working with the `doDiPhoMvaUpFront` flag.