Refactored editor templates for further reuse
Cleanup: No need for `previous_view_url`
Not all the context variables are necessary
Provide proper feedback in the admin page when validation fails
Added generic decorator for retrieving generic path objects

Supersedes the `get_translation_project` decorator, which only worked for
translation projects. The new decorator works for Language, Project, and
TranslationProject objects.
Added missing import
Added `permission_required` decorator

Apart from checking for `permission_codes` in the directory linked with
`path_obj` (or the root directory, if `path_obj` is not set), the current
request is populated with the current user's profile, the matching
permissions for the current directory, and the current `path_obj`.
Bye-bye boilerplate code!
Cleanup: moved decorator to a saner place