Service to write luminosity information to TTree when reading from FSRs

Sprucing writes FSRs containing the count of lumievents per run to the output mdf files. This draft will provide a service intended for use in DaVinci. The service will read the FSR when the input file is opened, create a list of pairs (run number, n_lumievents), merge any duplicated entry by run number, and write an output tree with two branches: runNumber and sumLumievents.

The user obtaining rootfiles from DaVinci jobs will hadd these rootfiles and obtain, in addition to the data, a tree with luminosity-by-run information.

Goes with DaVinci!937 (merged).