Introduction of prepare_data.sh

Script prepare_data.sh runs official CbmRoot macros to produce simulation chain from UrQMD input to reconstruction.

User can specify input options such as collision system, energy, centrality, setup performance and events-handling type (eb/tb) in a section "User settings". All the data is saved to DATA_DIR directory, which is also should be specified.

Also, one can specify L1Algo condition name, so the QA L1_histo_*.root files for different modes will be saved into the condition-specific directory. Example:

$ ./prepare_data.sh -s default

will create a directory ${DATA_DIR}/reco_default/, in which all the L1_histo*.root would be saved.

Processing of transportation and digitization parts by default is carried out only, if the corresponding output data files were not created before and saved to the ${DATA_DIR}. But one still can force digitization applying --rerun-digi option:

$ ./prepare_data.sh -s snapshot_one --rerun-digi