Cherry-pick MR !278 to master branch
Ostap: add utilities to fit the efficiency from unbinned samples using RooEfficiency
See merge request !278 (merged)
(cherry picked from commit 73194870)
7a68262f Ostap: add fits for efficienciy from unbinned samples using RooEfficiency bc4a1b24 Ostap: f62b253d small addition 8ea8a390 tiny fix 4b528681 add max-lookup through "mode"-function d19a89c1 tiny addition cd1d210f make it better