Modular-Kicad milestone B), major portions:

*) Rework the set language support, simplify it by using KIWAY.  Now any major
   frame with a "change language" menu can change the language for all KIWAY_PLAYERs
   in the whole KIWAY.  Multiple KIWAYs are not supported yet.

*) Simplify "modal wxFrame" support, and add that support exclusively to
   KIWAY_PLAYER where it is inherited by all derivatives.  The function
   KIWAY_PLAYER::ShowModal() is in the vtable and so is cross module capable.

*) Remove the requirements and assumptions that the wxFrame hierarchy always
   had PCB_EDIT_FRAME and SCH_EDIT_FRAME as immediate parents of their viewers
   and editors. This is no longer the case, nor required.

*) Use KIWAY::Player() everywhere to make KIWAY_PLAYERs, this registers the
   KIWAY_PLAYER within the KIWAY and makes it very easy to find an open frame
   quickly.  It also gives control to the KIWAY as to frame hierarchical
   relationships.

*) Change single_top to use the KIWAY for loading a KIFACE and instantiating
   the single KIWAY_PLAYER, see bullet immediately above.

*) Add KIWAY::OnKiwayEnd() and call it from PGM_BASE at program termination, this
   gives the KIFACEs a chance to save their final configuration dope to disk.

*) Add dedicated FRAME_T's for the modal frames, so m_Ident can be tested and
   these modal frames are distinctly different than their non-modal equivalents.
   KIWAY_PLAYER::IsModal() is !not! a valid test during the wxFrame's constructor,
   so this is another important reason for having a dedicated FRAME_T for each
   modal wxFrame.

On balance, more lines were deleted than were added to achieve all this.

common/basicframe.cpp

@@ -169,12 +169,8 @@ void EDA_BASE_FRAME::ReCreateMenuBar()
 }
 
 
-void EDA_BASE_FRAME::SetLanguage( wxCommandEvent& event )
+void EDA_BASE_FRAME::ShowChangedLanguage()
 {
-    int id = event.GetId();
-
-    Pgm().SetLanguageIdentifier( id );
-    Pgm().SetLanguage();
     ReCreateMenuBar();
     GetMenuBar()->Refresh();
 }
@@ -717,27 +713,3 @@ void EDA_BASE_FRAME::CheckForAutoSaveFile( const wxFileName& aFileName,
     }
 }
 
-
-void EDA_BASE_FRAME::SetModalMode( bool aModal )
-{
-    // Disable all other windows
-#if wxCHECK_VERSION(2, 9, 4)
-    if( IsTopLevel() )
-    {
-        wxWindowList::compatibility_iterator node = wxTopLevelWindows.GetFirst();
-
-        while( node )
-        {
-            wxWindow* win = node->GetData();
-
-            if( win != this )
-                win->Enable( !aModal );
-
-            node = node->GetNext();
-        }
-    }
-#else
-    // Deprecated since wxWidgets 2.9.4
-    MakeModal( aModal );
-#endif
-}