refactor: move bdb (bitdb) interaction from init.cpp to wallet.cpp

this will remove db.h from init.cpp

src/wallet/wallet.h

@@ -743,6 +743,12 @@ public:
     //! Get wallet transactions that conflict with given transaction (spend same outputs)
     std::set<uint256> GetConflicts(const uint256& txid) const;
 
+    //! Flush wallet (bitdb flush)
+    void Flush(bool shutdown=false);
+
+    //! Verify the wallet database and perform salvage if required
+    static bool Verify(const std::string walletFile, std::string& warningString, std::string& errorString);
+    
     /** 
      * Address book entry changed.
      * @note called with lock cs_wallet held.