move search string handling to admin.js
make config names more precise and consistent
set setting for predefined_news_type_id
simplify model and migrate schema

• remove service_id because services don't need to be handled specially (a event category can be used)
• add migration script to change database
• rename this.content to this._element to fit current coding style
• cleanup
remove unnecessary methods and cleanup

• add arg to method make it consistent
  if externally managed categories can be excluded, you should be able to overwrite this for the input widget
refactor loading of list widgets WIP

• load list widgets only on changing the accordion tab
	this only works when a widget is loaded the first time and the tabs are clicked the first time