Display class hierarchies in the browser

[dmatveev]

Currently all classes in a namespace are displayed as a plain list. It would be much more convenient if the classes were displayed hierarchically, with the root classes in the hierarchy leftmost, and its subclasses indented to right (according to the inheritance level). Example:

Object
  Behavior
    ClassDescription
      Class
      Metaclass

It will require a protocol change, since currently no information about class relationships is transferred.