Add support for multi-user decryption

* Add CLI support using the command "twrp decrypt <PASSWORD> [USER ID]"
* Add GUI support using the menu Advanced --> Decrypt User

Change-Id: Id2681bc2b1012a0571417f7a6e0b980b1b25c61c
(cherry picked from commit 5a79f67a1b1bd1bcadeca0a4896a871646652534)
diff --git a/crypto/ext4crypt/Ext4Crypt.h b/crypto/ext4crypt/Ext4Crypt.h
index 57623e3..beb5d8f 100644
--- a/crypto/ext4crypt/Ext4Crypt.h
+++ b/crypto/ext4crypt/Ext4Crypt.h
@@ -38,7 +38,7 @@
 bool e4crypt_unlock_user_key(userid_t user_id, int serial, const char* token, const char* secret);
 //bool e4crypt_lock_user_key(userid_t user_id);
 
-bool e4crypt_prepare_user_storage(const char* volume_uuid, userid_t user_id, int serial, int flags);
+//bool e4crypt_prepare_user_storage(const char* volume_uuid, userid_t user_id, int serial, int flags);
 //bool e4crypt_destroy_user_storage(const char* volume_uuid, userid_t user_id, int flags);
 
 bool lookup_key_ref(const std::map<userid_t, std::string>& key_map, userid_t user_id,