Opening dirs in file viewer should redirect to browser

[dshoreman]

If you pass a directory to the file editor, e.g. /files/edit/?f=%2Ftmp it will attempt to open it as if it were a file.
The result is an "Unsupported filetype directory" error.

Instead, that error should be caught (probably in the vue route handlers) so that it can redirect to the same path without edit/. Likewise, if ?f is an empty string or not set at all, it should redirect to /files.