Mallard Guard client enforcement

To use your client settings as the server's enforced values, copy
config/mallard_guard/client.toml here as client.toml. On a dedicated server,
copy the client.toml from your Minecraft installation to this server's
config/mallard_guard/enforce/ folder. Enable enforcement in game as an OP.

When this template exists, it supplies the Enforce screen's values.
Applying changes in that screen also updates the copied client.toml.
The categories marked Don't Enforce still start with these values,
but players can edit them afterward. The original client file is not changed.
