Add query component to scm URL

Previously when constructing a scm URL from a path, if scm was not enabled
we returned a file URL. This could result in some unexpected behavior.
For instance, when a directory was selected in the file browser,
activating "SCM Status" would just open the untracked directory.
This patch, insteads, adds a query to the scm URL that can be parsed to
determine how to handle the scm status request later on.