make logging use python style format

[a-teammate]

Most of the logging calls have been reformatted in stream style (bc the intermediate solution in the logging branch needed stream style calls for everything).

However in a lot of places this obfuscates the code without need.

E.g.

spdlog::get("global")->info() << "invalid frame " << frame << ", range " << range << " in model " << model->name;

should be rewritten in python style (see wiki) to be actually readable:

spdlog::get("global")->info("invalid frame {}, range {} in model {}", frame, range, model->name);

( less obfuscated parts are ofc not a problem, e.g.

spdlog::get("global")->debug() << "Using home directory: " << dir;

could stay stream style)