build: Add --disable-bip70 configure option

This patch adds a --disable-bip70 configure option that disables BIP70
payment request support. When disabled, this removes the dependency of
the GUI on OpenSSL and Protobuf.

src/qt/walletmodeltransaction.h

@@ -8,6 +8,7 @@
 #include <qt/walletmodel.h>
 
 #include <memory>
+#include <amount.h>
 
 #include <QObject>