code: def register(PluginClass):
      
      if PluginClass in _cache.keys():
          raise Exception("Plugin class already registered")
      plugin = PluginClass()
      _cache[PluginClass] = plugin
  
      if getattr(PluginClass, 'extra_page_actions', False):
          for key in plugin.extra_page_actions:
              if key not in _extra_page_actions:
                  _extra_page_actions[key] = []
              _extra_page_actions[key].extend(plugin.extra_page_actions[key])
  
      if getattr(PluginClass, 'extra_edit_actions', False):
          for key in plugin.extra_edit_actions:
              if key not in _extra_edit_actions:
                  _extra_edit_actions[key] = []
              _extra_edit_actions[key].extend(plugin.extra_edit_actions[key])
  
  
      if getattr(PluginClass, 'navbar_links', False):
          _navbar_links.extend(list(plugin.navbar_links))
docs: Register a plugin class. This function will call back your plugin's
      constructor.