Adding fragments for BsTauTau in ttbar analysis

[friti]

Hello!

This PR adds the fragment needed for the MC production of the BsTauTau signal in ttbar, which has already been used for the central MC production here.

Additionally, it includes other fragments with different Bs and Bs* mass points for MC productions aimed at mass regression of the Bs meson.

Below is the difference between the baseline fragment ttbarBsTauTau_fragment.py and the modified fragment with a Bs mass point of 5.5 GeV, ttbarBsTauTau_bsmass_5p5gev_fragment.py.

16c16
<             particle_property_file = cms.FileInPath('GeneratorInterface/EvtGenInterface/data/evt_2014_bsmass_5p5gev.pdl'),
---
>             particle_property_file = cms.FileInPath('GeneratorInterface/EvtGenInterface/data/evt_2014.pdl'),
41,42d40
<             '531:m0 = 5.5',  # override Bs mass in Pythia
<             '533:m0 = 5.54983', # override Bs* mass in Pythia

The MR for the updated pdl files is here MR#28.

Please let me know if something else is needed from my side.

Thanks a lot,
Federica for the analysis team.