Subtract fee from amount

Fixes #2724 and #1570.

Adds the
automatically-subtract-the-fee-from-the-amount-and-send-whats-left
feature to the GUI and RPC (sendtoaddress,sendmany).

src/qt/coincontroldialog.h

@@ -43,6 +43,7 @@ public:
 
     static QList<CAmount> payAmounts;
     static CCoinControl *coinControl;
+    static bool fSubtractFeeFromAmount;
 
 private:
     Ui::CoinControlDialog *ui;