makes the login experience a bit friendlier to non-developer users

* new route `/edit?url=` intended to be used as an edit button target, which detects the type of post and redirects to the appropriate editing interface
* implemented the edit interface for favorites

update to "create" scope by default, but allow the user to choose "post" as a fallback. also updates indieauth/client to 0.2 for json support.

* looks for a media endpoint in the micropub config
* if media endpoint is available, both the note interface and the editor will upload files to it instead of posting the photo directly
* the note interface autosaves in-progress notes in localstorage