It should be split into two pieces: configuration file management
(loading/saving/renaming/deleting) and calling into wg-quick via
RootShell. The configuration file management part should then go
back into the main package. This is in preparation for adding
additional backends based on wg(8) and wireguard-go.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>