Render the block settings form where needed

Problem/Motivation

It would be nice to have the block settings form rendered in the "HomeboxPortletTypeBlock" "buildThirdPartyConfigurationForm()" and "getBlockPlugin()" methods.

See https://www.drupal.org/project/block_field → on how to do that.

Steps to reproduce

Proposed resolution

Render block settings form where needed.

Remaining tasks

User interface changes

API changes

Data model changes