Improve compile times

[mgeplf]

xxBase.h is included in many TUs, and its compile time is quite heavy: 2.42s on my machine. Since there are ~1200 TUs, that's almost 3000s of compile time:

Not everything is needed; for instance, the template instantiations (the blue 'icicles' in the above screenshot) required for all the iterators costs about 860ms, and many are use only a couple times.

Including list, vector, valarray, map, fstream and iostream combined take about 800ms.

Cleaning this up would be a big win for compile times, and thus programmer efficiency.

[mgeplf]

Timing trace file for the above:
xxBase.cpp.json.gz