ClinchedDBValues rework

[yakra]

• Speed (C++)
  • [ ] Store arrays of containers, lose the mutexes.
• Speed + RAM (C++, Py)
  • [x] Instead of strings, store the individual data used to construct them. This may work well on epoch, with its 512K L2 cache. How might .sql file write times be affected?
• RAM (C++, Py)
  • [x] ~Can anything be doubled up between tables?~ Nope!
• Organization (C++)
  • [ ] Consider static variables as mentioned in https://github.com/TravelMapping/DataProcessing/issues/378#issuecomment-747730068. (Why did I not implement that? Was it just that it's lower impact? How often is a ClinchedDBValues passed around?) Would need an init(int) function to set up the arrays to the right size.
  • [ ] The C++ implementation as a matter of practicality has diverged a bit from the Python implementation, in terms of how things are named & structured. I forget exactly how. Will this make it easier to bring their names & structure more in line?

---

Comments @ https://github.com/TravelMapping/DataProcessing/issues/304#issuecomment-619171708 indicate the Speed + RAM strategy may chasing after diminishing returns, but OTOH, from #132:

Rather than reopen TravelMapping#304, I'll just leave a note here. sulogs/speedrecord.sh indicates a few speed records here relative to what went on before; 39.2s vice 40.6. May be worth looking into after all?

---

The Speed strategy is new and may be worth pursuing.