Support new Hackage in the hackage-mirror tool

Support the new Hackage server by default in the `hackage-mirror` tool:

* Use the new Hackage routes by default. The option `--src-is-old-hackage` can be used to indicate that the source is the old Hackage server so that the old routes are used.

* Disable mirroring the uploaders by default. You can optionally enable it using the `--mirror-uploaders` option.