Add support mode for dark mode to SCINTILLA_TRICKS.

Also removes the return value from the BITMAP_STORE's themeChanged
method as it will provide the wrong answer for the second frame it's
called on.

Also hooked up ACTION_TOOLBAR, the app launcher, and the project tree
to the wx event for system color changes so they change on the fly.

Fixes https://gitlab.com/kicad/code/kicad/issues/6026

common/bitmap_store.cpp

@@ -164,11 +164,10 @@ wxImage BITMAP_STORE::getImage( BITMAPS aBitmapId, int aHeight )
 }
 
 
-bool BITMAP_STORE::ThemeChanged()
+void BITMAP_STORE::ThemeChanged()
 {
     COMMON_SETTINGS* settings = Pgm().GetCommonSettings();
-
-    wxString oldTheme = m_theme;
+    wxString         oldTheme = m_theme;
 
     if( settings )
     {
@@ -186,9 +185,8 @@ bool BITMAP_STORE::ThemeChanged()
         m_theme = wxT( "light" );
     }
 
-    m_bitmapNameCache.clear();
-
-    return !oldTheme.IsSameAs( m_theme );
+    if( !oldTheme.IsSameAs( m_theme ) )
+        m_bitmapNameCache.clear();
 }