refactored deck editor UI key shortcuts

The global shortcuts were removed in favor of key events
which are only triggered when a widget has focus. This is
necessary to allow different widgets to react differently
to the 'enter' key. The current key configuration is:
search edit focused:
  * left/right: decrease/increase card count for selected database card
  * enter: add selected card to deck
  * ctrl-enter: add selected card to deck sideboard
  * ctrl-left/right: decrease/increase card count in sideboard for selected card

database focused: the same as with search edit.

deckview focused:
  * left/right: decrease/increase card count for selected deckview card
  * enter: increase count for selected deckview card
  * delete/backspace: delete selected card from deck

cockatrice/src/keysignals.cpp

@@ -0,0 +1,49 @@
+#include "keysignals.h"
+#include <QKeyEvent>
+
+bool KeySignals::eventFilter(QObject * /*object*/, QEvent *event) {
+	QKeyEvent *kevent;
+
+	if(event->type() != QEvent::KeyPress)
+		return false;
+
+	kevent = static_cast<QKeyEvent *>(event);
+	switch(kevent->key()) {
+	case Qt::Key_Return:
+	case Qt::Key_Enter:
+		if(kevent->modifiers() & Qt::ControlModifier)
+			emit onCtrlEnter();
+		else
+			emit onEnter();
+		break;
+	case Qt::Key_Right:
+		if(kevent->modifiers() & Qt::ControlModifier)
+			emit onCtrlRight();
+		else
+			emit onRight();
+
+		if(!filterLROn)
+			return false;
+		break;
+	case Qt::Key_Left:
+		if(kevent->modifiers() & Qt::ControlModifier)
+			emit onCtrlLeft();
+		else
+			emit onLeft();
+
+		if(!filterLROn)
+			return false;
+		break;
+	case Qt::Key_Delete:
+	case Qt::Key_Backspace:
+		emit onDelete();
+
+		if(!filterDeleteOn)
+			return false;
+		break;
+	default:
+		return false;
+	}
+
+	return true;
+}