TextDocument.cpp: Fixed typo
BView: Don't allow a view to add itself as a child.
Make TextEditor referenceable.
TextDocumentView: Update TextEditor about certain changes
HaikuDepot: Some preparations for adding rating comments

* The package info area toggles a package's rating to a "Rate package..."
  button when the mouse hovers it.
* Clicking that button opens a window where one can enter a rating.
* Totally not working yet, but I want this in VCS.