Add CWallet::AddCryptedSaplingSpendingKey() hook

To be filled in when we implement Sapling persistence to disk.

src/wallet/wallet.h

@@ -999,7 +999,7 @@ public:
     bool RemoveViewingKey(const libzcash::SproutViewingKey &vk);
     //! Adds a viewing key to the store, without saving it to disk (used by LoadWallet)
     bool LoadViewingKey(const libzcash::SproutViewingKey &dest);
-    
+
     /**
       * Sapling ZKeys
       */
@@ -1007,6 +1007,8 @@ public:
     libzcash::SaplingPaymentAddress GenerateNewSaplingZKey();
     //! Adds Sapling spending key to the store, and saves it to disk
     bool AddSaplingZKey(const libzcash::SaplingSpendingKey &key);
+    bool AddCryptedSaplingSpendingKey(const libzcash::SaplingFullViewingKey &fvk,
+                                      const std::vector<unsigned char> &vchCryptedSecret);
 
     /** 
      * Increment the next transaction order id