Add additional information to FileRepo::getInfo

Add additional information to FileRepo::getInfo

The API's meta=filerepoinfo could use some additional information, most
pressingly a way to determine the MW API endpoint of the associated
repo. Since FileRepo already has scriptDirUrl (to which "/api.php" could
be appended), let's just add that.

And for good measure, we may as well include various other bits of
information that people might find useful.

Change-Id: I6d5aa6cf44ef1d9bdfd9b2f36f184e5fdc0900dd