Move ui_interface to bitcoin_server.a

There is no need for it in the utility libraries or tools.
Put it in init.cpp, and in the tests separately (as they can't link init).

src/init.cpp

@@ -62,6 +62,7 @@ enum BindFlags {
 };
 
 static const char* FEE_ESTIMATES_FILENAME="fee_estimates.dat";
+CClientUIInterface uiInterface;
 
 //////////////////////////////////////////////////////////////////////////////
 //