This was nasty.
Remove --block-rate-notify entirely; it's nearly useless on Oxen.
block and reorg notify remain, but now use a post-block hook rather than
shoving toxic Notify crap into cryptonote_core headers.
Remove misc_language.h: Half of it is unused, half of it is crap doesn't
need to be used, and the two useful things (median calculator and a
scope exit caller) were poorly written.
Rewrote median from scratch and moved it out of epee.
Simplified the scope exit handler and moved it to its own small header
in epee.
Converts all use of boost::filesystem to std::filesystem.
For macos and potentially other exotic systems where std::filesystem
isn't available, we use ghc::filesystem instead (which is a drop-in
replacement for std::filesystem, unlike boost::filesystem).
This also greatly changes how we handle filenames internally by holding
them in filesystem::path objects as soon as possible (using
fs::u8path()), rather than strings, which avoids a ton of issues around
unicode filenames. As a result this lets us drop the boost::locale
dependency on Windows along with a bunch of messy Windows ifdef code,
and avoids the need for doing gross boost locale codecvt calls.
