clipproperties: Disconnect from the project when it's closed

Closes #2171

Problem: When we open a new project via app menu, the current project gets closed but its reference in TransformationProperties class is not set to None.
1 job for clip-transformation-box-disappears in 7 minutes and 7 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #12943
build

00:07:07