Add split in new window action for editor views.

A few details are still to be done:
- extra windows are not restored yet
- window title of extra windows should show information about current
  editor
- the "raise main window" hack for Linux doesn't work with Qt 5

But it should already now be quite usable.

Change-Id: I638583ee4b2abe32e95c261bdf31b4a10b472748
Reviewed-by: David Schulz <david.schulz@digia.com>

src/plugins/coreplugin/coreconstants.h

@@ -105,6 +105,7 @@ const char ZOOM_WINDOW[]           = "QtCreator.ZoomWindow";
 
 const char SPLIT[]                 = "QtCreator.Split";
 const char SPLIT_SIDE_BY_SIDE[]    = "QtCreator.SplitSideBySide";
+const char SPLIT_NEW_WINDOW[]      = "QtCreator.SplitNewWindow";
 const char REMOVE_CURRENT_SPLIT[]  = "QtCreator.RemoveCurrentSplit";
 const char REMOVE_ALL_SPLITS[]     = "QtCreator.RemoveAllSplits";
 const char GOTO_OTHER_SPLIT[]      = "QtCreator.GotoOtherSplit";