* refactor: make tr_session_settings a libtransmission::Settings * refactor: make VariantConverter private in settings.cc
* refactor: add libtransmission::Settings * refactor: move RPC server's settings into tr_rpc_server::Settings * build: update project.pbxproj --------- Co-authored-by: Dzmitry Neviadomski <nevack.d@gmail.com>