Handle keyboard commands properly

It was hard-coded in TerminalDisplay.cpp - Shift+Up always results in
ScrollLineUpCommand regardless of settings in *.keytab. Now those
commands are correctly parsed by KeyboardTranslator.

Fixes lxde/qterminal#348

This fix is similar to KDE/konsole@b88dfb402a
while I use signals and slots instead of introducing new pointers. That
sounds more reliable :)

lib/Emulation.cpp

@@ -109,6 +109,10 @@ ScreenWindow* Emulation::createWindow()
 
     connect(this , SIGNAL(outputChanged()),
             window , SLOT(notifyOutputChanged()) );
+
+    connect(this, &Emulation::handleCommandFromKeyboard,
+            window, &ScreenWindow::handleCommandFromKeyboard);
+
     return window;
 }