fix some dialogs not having a parent window
fix creating windows bigger than screen

When creating a layout window, the window can not be bigger than the screen
If the layout window is created for the first time (=using default size defined
in the layout), the maximum width and height will be reduced to take into account
the size of potential decorations and panels
move code popping-up context menu for SongTree and SongList to a common function
disable manually editing autoupdated lists

The EditListButtons widget will now be hidden when the associated list is
in autoupdate mode