LHCBGAUSS-841: Modifications to EvtTauolaEngine for the B to tau tau physics analysis

Code changes to EvtTauolaEngine in EvtGen to allow the B to tau tau physics analysis to move forward:

1. It uses the updated BaBar hadronic currents by default. An extra decay file keyword TauolaCurrentOption can be used to reset the integer value via Tauola::setNewCurrents(). This means that if there is a build of Tauola with the intricate CLEO currents enabled, then the code will be able to use that by setting Define TauolaCurrentOption -1 in the decay file.

2. The code also allows the option to set the sub-branching fractions of certain modes via Tauola::setTaukle, which will improve MC generation efficiency by ignoring unneeded modes, using the decay file keywords TauolaBRx, where x = 1,2,3 or 4.

3. It also contains some code to artificially set the PDG ids of the tau parents to vector bosons to use internal Tauola spin matrix weights, but this is not enabled by default, since we believe it doesn't do the right spin physics for B decays (we need further feedback from the Tauola developers).

4. There is also new code in EvtParticle to allow the future storage and retrieval of double quantities, such as amplitude weights, via the setAttributeDouble(name, value) and value = getAttributeDouble(name) functions, although no decay model is using this at the moment and will therefore have zero effect on current MC production.

This code will be suitable for both the Sim09 and master branches.