Create attribution page

Using the metadata pulled down from the server, the bundler will call
out to parsoid to render a attribution page. The attribution page will
be added to the bundle as `attribution.html` (and optionally
`attribution.wt`) and a new metabook item will be added with type
'attribution'.

Relies on:
* https://gerrit.wikimedia.org/r/#/c/145189/
* https://gerrit.wikimedia.org/r/#/c/145192/

Change-Id: I85d578ef104d86beaf4d8d31b38794bc92c01c67
Respect metabook lang setting when localizing attributions page.

Change-Id: I090df946c7aac3c35322f8aab1c8169de8b5b05c
Fetch authors in larger batches; fetch authors for specific article revid.

Change-Id: Ic05e5d99ad4072416028b78aab8364ffdf237238
Skip wikitext fetch when `--no-compat` option is given.

The old pipeline used to parse the wikitext of the various image
pages, etc, in order to extract contributors and license information.
We have a dedicated API request for this now, so skip the unnecessary
wikitext fetch.

Change-Id: Ief3e447cd77607735d43ff7934bf8c949bc5e65b