LCG_95 Updates, master branch (2019.02.25.)

This is sort of a sibling of atlasexternals!445 (merged)...

I was able to build the Athena project against LCG_95 on top of the modifications from atlasexternals!445 (merged), and with these following changes. I also had to update the versions of the TDAQ externals in my build, and also the version of HEPUtils that Athena would pick up from LCG. But those updates should only be made when we actually switch the nightly to LCG_95.

For the Ttypes.h updates see: As the disappearance of Ttypes.h turned out to be a bit weird.

The boost_python -> boost_python27 name change was discussed quite a lot in the past. Since we only use boost_python in a single place in the offline code, this change in TrigConfDBConnection seemed the most practical. (This is different from how @rhauser implemented it for tdaq...)

The weirdest issue I came across was the one in G4UserActions. As I found in, apparently certain versions of G4 and Boost can catastrophically interfere with each other. 😦 This solution is very fragile, but it seemed the most practical for now. @jchapman, we should probably think of something smarter later on though...

@emoyse, @wlampl, with these updates added, I believe that updating to LCG_95 will be just a question of updating to a newer version of atlasexternals, and switching the version of some of the other externals that we use.

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