Handle bundle file modifications on external template removal

Currently when removing an external template that, the corresponding bundle.html file is entirely removed

=> this can lead to lost configuration if users made some changes in it in the meantime

AC

• When an external template is removed, the bundle.html file should be kept if changes were made in it as well as the reference in the main bundle.html file
• If no changes were made, the bundle.html is removed and its reference in the main bundle file as well