message: PanelHeaderButton: bring back line-height
  for primitive buttons
diff: .PanelHeaderButton--android.PanelHeaderButton--primitive {
  height: 48px;
  + line-height: 48px;
  padding: 0 12px;
  }
  .PanelHeaderButton--vkcom.PanelHeaderButton--primitive {
  height: 48px;
  + line-height: 48px;
  padding: 0 10px;
  }
  