Avoid ugly flash of small window during startup.

Electrum 2.x flashes a small window during startup before the main window appears.
This turns out to be the fee edit box being enabled in create_send_tab().
Setting it to visible when the grid containing it is unparented causes QT to actually
display a window with just the edit box widget for some reason.  So defer the
call to set its visibility until the grid is parented.

gui/qt/main_window.py

@@ -922,7 +922,6 @@ class ElectrumWindow(QMainWindow):
         self.fee_e = BTCAmountEdit(self.get_decimal_point)
         grid.addWidget(self.fee_e_label, 5, 0)
         grid.addWidget(self.fee_e, 5, 1, 1, 2)
-        self.update_fee_edit()
 
         self.send_button = EnterButton(_("Send"), self.do_send)
         self.clear_button = EnterButton(_("Clear"), self.do_clear)
@@ -987,6 +986,9 @@ class ElectrumWindow(QMainWindow):
         vbox.addWidget(self.invoices_label)
         vbox.addWidget(self.invoices_list)
 
+        # Defer this until grid is parented to avoid ugly flash during startup
+        self.update_fee_edit()
+
         run_hook('create_send_tab', grid)
         return w