enable async refresh

src/wallet/api/wallet.cpp

@@ -435,6 +435,10 @@ WalletImpl::WalletImpl(NetworkType nettype, uint64_t kdf_rounds)
 
     m_refreshIntervalMillis = DEFAULT_REFRESH_INTERVAL_MILLIS;
 
+    m_refreshThread = boost::thread([this] () {
+        this->refreshThreadFunc();
+    });
+
 }
 
 WalletImpl::~WalletImpl()