Added "ENTER" to join a room

Can now join a room by highlighting a room and pressing ENTER. Works
nice with arrow navigation.

cockatrice/src/gameselector.cpp

@@ -77,6 +77,7 @@ GameSelector::GameSelector(AbstractClient *_client, const TabSupervisor *_tabSup
     connect(joinButton, SIGNAL(clicked()), this, SLOT(actJoin()));
     connect(spectateButton, SIGNAL(clicked()), this, SLOT(actJoin()));
     connect(gameListView, SIGNAL(doubleClicked(const QModelIndex &)), this, SLOT(actJoin()));
+    connect(gameListView, SIGNAL(activated(const QModelIndex &)), this, SLOT(actJoin()));
 }
 
 void GameSelector::actSetFilter()