Lower the image updating for theme into GUIPrefs::Commit()...

... weakening dependency of PrefsDialog.cpp on particular preference page
implementations

src/prefs/GUIPrefs.cpp

@@ -269,6 +269,10 @@ bool GUIPrefs::Commit()
       gPrefs->Flush();
    }
 
+   // Reads preference /GUI/Theme
+   theTheme.LoadPreferredTheme();
+   ThemePrefs::ApplyUpdatedImages();
+
    return true;
 }
 

src/prefs/PrefsDialog.cpp

@@ -68,7 +68,6 @@
 #include "MidiIOPrefs.h"
 #endif
 
-#include "../Theme.h"
 #include "../widgets/HelpSystem.h"
 
 #if wxUSE_ACCESSIBILITY
@@ -813,10 +812,6 @@ void PrefsDialog::OnOK(wxCommandEvent & WXUNUSED(event))
    }
    gPrefs->Flush();
 
-   // Reads preference /GUI/Theme
-   theTheme.LoadPreferredTheme();
-   ThemePrefs::ApplyUpdatedImages();
-
    SavePreferredPage();
 
 #if USE_PORTMIXER