Ways to reduce divergence with upstream, to ease merging

There is some discussion about this in various places (#935, #964), but I wanted to make a dedicated issue to propose things I'm running into while reviewing merges in #935.

One thing I've talked to someone about, I forget who -- right now in our build stuff (configure/make), a lot of things were renamed from 'bitcoin' to 'elements', but also a lot of things were not. I think probably the thing that would make this easiest for future maintenance would be to minimize the diff from upstream, by ONLY using 'elements' in places where it's user-facing (file/directory/target names), and revert all the names of purely-internal variables (some of which were changed, and some of which were not) back to 'bitcoin'.

Lisez la discussion dans les issues #935 et #964, puis examinez les fichiers de build configure et make où des noms ont été changés de « bitcoin » à « elements ». Comparez ces changements avec upstream et identifiez quels noms sont user-facing et lesquels sont internes ; le travail est terminé lorsqu’une proposition ciblée ou une modification coordonnée réduit les divergences inutiles sans changer les noms user-facing.