PWGPP-3, PWGPP-4 - Reducing the size of the output containers with points (Correspon...

PWGPP-3, PWGPP-4 - Reducing the size of the output containers with points  (Corresponding UnitTest in separate commit))
0.) Downsaling factor controlled by  SetFriendDownscaling expressed in number of entries or relative size
1.) Use 0 pointer instead of zerro content (zip not efficent)
2.) Removing dummy friend track info from all exporting trees

AliAnalysisTaskFilteredTree.{h,cxx}