Add support for new unified configuration handling

[asarium]

The current antipodes branch has a new configuration system that now uses ini files on all platforms. It also uses a new user specific directory for writing all files at runtime instead of writing them to the current directory. This directory us determined by SDL_GetPrefPath.

These changes add support for that new behavior. This includes migrating old data to the new location by copying pilot files and old configuration data.

[asarium]

Conflicts have been resolved.

[IssMneur]

committed in 384215c6a9c61dc6e9effcd9982815dad7478366 and related.