Fix the ``changeEmail`` method's invocation signature of ``can.edit``,
and fix the definition of ``can.edit`` to allow it to work with users as
the "item".
Note that this relies on "_id" to be unique across collections. Mongo
won't generate the same ID in two collections, but it is possible to
manually add an object to another collection with a duplicate ID.
Switched everything over to use can.* functions from telescope-lib instead of using can* functions from lib/permissions.js, deleted lib/permissions.js, added some tests for permissions, and some other random cleanup like deleting unused code.
Conflicts:
client/views/comments/comment_form.js
