add example macros and class templates for running flow package analysis on a ttree...

add example macros and class templates for running flow package analysis on a ttree in ROOT

commit consists of three things:
a) two macros (in macros folder)
- run: runs (in aliroot) and fills a ttree with kinematic info from alivevent
- read: reads (in just root) the ttree info and performs a flow analysis with the flow package

b) two analysis classes
- AliAnalysisTaskTTreeFilter -> analysis task for AliROOT which converts input events to ttree
- AliFlowEventSimpleFromTTree -> task for ROOT, fills flow events with ttree input

c) two helper classes which should serve as a starting point
- AliFlowTTreeEvent : simple event class
- AliFlowTTreeTrack: simple track class

as these are helper classes designed to get the user started, they are not compiled by default. the run and read macro will compile on-the-fly