Qt: make all menus modal

This fixes a lot of problems where a menu or a text window was up
and the main window accepted input - for example you could move around,
making another window of the same type pop up ...

doc/fixes3-7-0.txt

@@ -2145,6 +2145,7 @@ Qt: {maybe just Qt+macOS:} when viewing a text window ('V' to look at 'history'
 	window got pushed underneath the main window so seemed to go away
 Qt: use idPressed signal instead of buttonPressed and mappedString instead
 	of mapped for recent Qt (pr #913 by chasonr)
+Qt: make all NetHack menu and text windows modal
 Qt: support Unicode supplementary characters (pr #1047 by chasonr)
 Qt: qt_tilewidth and qt_tileheight are allocated with alloc() and need to be
 	freed with free(); don't use qt_tilewidth and qt_tileheight after

win/Qt/qt_menu.cpp

@@ -220,6 +220,7 @@ NetHackQtMenuWindow::NetHackQtMenuWindow(QWidget *parent) :
             this, SLOT(TableCellClicked(int,int)));
 
     setLayout(grid);
+    setModal(true);
 }
 
 NetHackQtMenuWindow::~NetHackQtMenuWindow()
@@ -1013,6 +1014,7 @@ NetHackQtTextWindow::NetHackQtTextWindow(QWidget *parent) :
     setFocusPolicy(Qt::StrongFocus);
     // needed so that keystrokes get sent to our keyPressEvent()
     lines->setFocusPolicy(Qt::NoFocus);
+    setModal(true);
 }
 
 void NetHackQtTextWindow::doUpdate()