VpnService: Move it to a backends package

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>

app/src/main/java/com/wireguard/android/BaseConfigFragment.java

@@ -3,6 +3,7 @@ package com.wireguard.android;
 import android.app.Fragment;
 import android.os.Bundle;
 
+import com.wireguard.android.backends.VpnService;
 import com.wireguard.config.Config;
 
 /**