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.h

@@ -0,0 +1,30 @@
+#include <QObject>
+#include <QEvent>
+
+class KeySignals : public QObject {
+	Q_OBJECT
+
+private:
+	bool filterDeleteOn;
+	bool filterLROn;
+
+signals:
+	void onEnter();
+	void onCtrlEnter();
+	void onLeft();
+	void onCtrlLeft();
+	void onRight();
+	void onCtrlRight();
+	void onDelete();
+
+protected:
+	virtual bool eventFilter(QObject *, QEvent *event);
+
+public:
+	KeySignals()
+		: filterDeleteOn(true)
+		, filterLROn(true)
+		{}
+	void filterDelete(bool on) { filterDeleteOn = on; }
+	void filterLeftRight(bool on) { filterLROn = on; }
+};