refs #803

closes #1139

autopep8 -i --select=W602
Also some other minor deprecated syntax changes, like "while 1".
I did not commit the less obvious changes.

refs #806

[weboorrents] temporary modification to fully load torrent on 'info short_id'

This is recommended by Debian.
closes #618

* Remove callbacks in Collection object
  Make Collection a "dumb" object (and also a base object,
  though it isn't very useful for now)
* Rename Path to WorkingPath, because it is more about managing state
  than being a single path.
* Rewrite almost all WorkingPath, because the code was overly
  complicated for no reason (I tried some special cases and it turned
  out that fromstring didn't handle them, and that the
  quote-escape-unquote was just unecessary). I also rewrote it to be
  more pythonic (no more lambdas and maps) and added tests.
* Require the full split path when creating a Collection. Because, come to
  think of it, an object needs an unique identifier; in the case of
  Collections, it is the full path, not only its last part.
  I might even replace the id by the full split path in the future.
* There is now only one way to get items of a Collection: calling
  iter_resources().
* Rewrite flatten_resources to iter_resources_flat(), which just calls
  ite...

Use stderr and return codes >0 when it makes sense.
Loose return code conventions:
* 1 for generic errors
* 2 for user input errors
* 3 for remote errors (not found, etc.)
* 4 for not implemented