message: Make AttentionBar checkbox use less space
  Put it under the buttons, not to their ride. This makes the bar taller,
  but easier to read.
diff: @@ -110,9 +110,16 @@ AttentionBar::AttentionBar(wxWindow *parent)
  labelSizer->Add(m_explanation, wxSizerFlags().Expand().Border(wxTOP|wxRIGHT, PX(4)));
  sizer->Add(labelSizer, wxSizerFlags(1).Center().PXDoubleBorder(wxALL));
  sizer->AddSpacer(PX(20));
  - sizer->Add(m_buttons, wxSizerFlags().Center().Border(wxALL, SMALL_BORDER));
  - sizer->Add(m_checkbox, wxSizerFlags().Center().Border(wxRIGHT, BUTTONS_SPACE));
  - sizer->Add(btnClose, wxSizerFlags().Center().Border(wxALL, SMALL_BORDER));
  + auto allButtonsSizer = new wxBoxSizer(wxHORIZONTAL);
  + auto buttonsAndCheckboxSizer = new wxBoxSizer(wxVERTICAL);
  + sizer->Add(buttonsAndCheckboxSizer, wxSizerFlags().Center().Border(wxTOP, PX(1)));
  + buttonsAndCheckboxSizer->Add(allButtonsSizer, wxSizerFlags().Expand());
  + buttonsAndCheckboxSizer->Add(m_checkbox, wxSizerFlags().Left().Border(wxTOP, MACOS_OR_OTHER(PX(2), PX(4))));
  + allButtonsSizer->Add(m_buttons);
  + allButtonsSizer->AddStretchSpacer();
  + allButtonsSizer->AddSpacer(SMALL_BORDER);
  + allButtonsSizer->Add(btnClose, wxSizerFlags().Center().Border(wxTOP, PX(1)));
  + allButtonsSizer->AddSpacer(SMALL_BORDER);
  #ifdef __WXMSW__
  sizer->AddSpacer(PX(4));
  #endif
  