A type doesn't need to extend a type.

Also extracting a method.

ID is used like identifier

Deletion of property/type is done via PATCH method by setting 'deleted' flag of the property/type
Properties/types, with deleted flag set, are not visible to user.

- If no type is selected, main content is empty
- Deleting panel version of index template
- Using associative array also for the menu
- Using new view variable "selectedTypeId" for making visual selection in the menu

For the menu on the left, only type names and ids are fetched. When a type is clicked, more data is shown about the type in right part of the page. By typeId, additional type data is fetched (including properties).

Important notice: uriPattern: '{@controller}(/{@action})' exists also in Forger package, and that makes conflict. To solve it, SGalinski.TypoScriptReferenceFrontend routes should be included in main Routes.yaml file before forger routes. And it should be prefixed in main Routes.yaml file like this: uriPattern: 'ts/<SGalinski.TypoScriptReferenceFrontend>'