Implement direct boot awareness

To do direct boot, important files need to be moved to device storage (i.e. not as safe storage). The only thing sensitive is user credentials (server settings in each profile) and the config file passed to libss-*.so. In order to implement direct boot, at least the active profile has to be moved/copied to device storage.

This commit keeps profile information (and temporary data used by ProfileConfigFragment) and Shadowsocks config in credential storage and move everything else to device storage. In order to make direct boot work, active profile is also copied into device storage and Shadowsocks config file is created in device storage during direct boot. Cleanup of those information is also implemented.

Fixes #1457.

NB:

* `android:directBootAware` can't be used on application element. That seems to be used by system apps.
* Works fine with multi-user;
* Old GSM files are not migrated (see App.kt) to device storage.

mobile/src/main/java/com/github/shadowsocks/utils/Constants.kt

@@ -21,7 +21,11 @@
 package com.github.shadowsocks.utils
 
 object Key {
-    const val PROFILE = "profile.db"
+    /**
+     * Public config that doesn't need to be kept secret.
+     */
+    const val DB_PUBLIC = "config.db"
+    const val DB_PROFILE = "profile.db"
 
     const val id = "profileId"
     const val name = "profileName"
@@ -39,6 +43,7 @@ object Key {
     const val route = "route"
 
     const val isAutoConnect = "isAutoConnect"
+    const val directBootAware = "directBootAware"
 
     const val proxyApps = "isProxyApps"
     const val bypass = "isBypassApps"