Add PlainTreeFiller and TaskManager features

[lubynets]

PlainTreeFiller:

• add possibility to rename fields which are copy-pasted from AnalysisTree into plain branch;
• add warnings when one tries to ignore, preserve or rename field which does not exist

TaskManager:

• add possibility to Run() starting not from 0-th event, but from arbitrary one (like in e.g. CbmRoot):

• Run() - run all events;
• Run(N) - run N events starting from 0-th;
• Run(M, N) -run N events starting from M-th.

Minor changes:

• add function GetObjectWithNullptrCheck() to HelperFunctions.hpp
• add consts to autos in range-based for loops where applicable.