SetActionVisible
void SetActionVisible(uint32 command, bool visible);
fToolBar->SetActionVisible(M_UNREAD, true);
fToolBar->SetActionVisible(M_READ, false);
fToolBar->SetActionVisible(M_UNREAD, false);
fToolBar->SetActionVisible(M_READ, true);
fToolBar->SetActionVisible(M_UNREAD, false);
fToolBar->SetActionVisible(M_READ, false);
fToolBar->SetActionVisible(MSG_FULL_SCREEN, fFullScreen);
fToolBar->SetActionVisible(MSG_FULL_SCREEN, false);