Merge pull request alisw#180 from qgp/update_doc

Update PWG-MM README

Checkpoint history rewrite

CaloPhotonCuts: tune NL params

few fixes & additions here and there...

check ratio Ecell lead over E cluster vs number of local maxima

User-settable TF1 for mass mean, sigma (which then avoids initial fit…

… to ensure speed + stability)

added support for 'hybrid approach'

Bug Fix in Histogram

Change to THnSparse

3D histograms in this task expected to be sparsely filled,
in particular for min. bias events. In this case THnSparse
is more efficient in memory consumption compared to a TH3.

Implement reading of the downscale factors from OCDB

Downscale factors can be read from the OCDB and converted
into the format used in this task.
- Support only for EMCAL trigger (EMC7 in case of L0) and INT7
- Trigger class expected to be present only in one cluster (cluster
  definition not handled). If present more than once the first
  occurrence is used