Different threads are adding and calling callbacks, so this should have
some locking. This is both to ensure thread safety when accessing
`s_callbacks` and to ensure that there won't be situations where a
callback gets called after it's removed.

`s_callback_guards` is also accessed from multiple threads and has
therefore been made atomic.

In LabelMap.cpp, the code is currently unused so I was unable to test it.

In WiiUtils.cpp, the magic value `1u` was replaced by the constant value `DiscIO::PARTITION_UPDATE`.

This file was only used by DolphinWX. DolphinQt uses Qt.ini instead.

This way you can't mix up regular config callback IDs and CPU thread
config callback IDs. (It would be rather bad if you did!)

This fixes a problem that started happening in CoreTimingTest after the
previous commit. CPUThreadConfigCallback registers a Config callback
only once per run of the process, but CoreTimingTest calls
Config::Shutdown after each test, and Config::Shutdown was clearing all
callbacks, preventing the callback from running after that.

Added AchievementSettings in Config with RA_INTEGRATION_ENABLED, RA_USERNAME, and RA_API_TOKEN. Includes code to load and store from Achievements.ini file in config folder.