Adds "releases" landing page, ties in to the /dist versions JSON

[snostorm]

For #284

Builds on #276 (PR is against that branch right now.) This page is auto-generated based on contents of https://iojs.org/dist/index.json - which is downloaded at the start of the build and develop tasks. We're pulling from https://iojs.org/dist/index.json so the build team can automatically trigger site updates when a new version rolls out.

The current (simple) layout to get the ball rolling.

• Eventually I'd like the Changelogs to be mirrored on the site.
• Better download links (per platform, etc.). Maybe each version has a landing page, tied to the change log?
• It would be nice to group by major/minor (so the v1.5.x, v1.4.x, etc. are visually grouped together.)?

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I restructured the download task for multiple files. Added two external markdown files (governance, working-groups) which could be imported for automatic, up-to-date inclusion on the website.

If testing locally you'd see these downloaded files on /en/working-groups.html and /en/governance.html.

Outstanding question there: how to easily let the i18n groups import their own targets this way. Also, how do we let them point at external release notes, etc. (Unless we opt to include these in the site as well, which I am in favour of to keep things simple.)

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Added a "Releases" link to the footer nav, for now.

[snostorm]

Originally #287 but that was targeting the wrong branch.

[snostorm]

The layout has been updated. Here's a copy of the OLDER layout for reference.

The NEW one (in the main PR description) is fairly responsive. On mobile the three links appear below the other information (npm, v8 version.)

[snostorm]

@Fishrock123@therebelrobot I'll ping my two go-to build guys on this one. Functionally the release page is ready.

Might need a cleanup / decision on the inclusion of the governance, working group pages (like, if we should link them, etc. or just remove from the "download" for now) before merging.

[snostorm]

@Fishrock123

I restructured the download task for multiple files. Added two external markdown files (governance, working-groups) which could be imported for automatic, up-to-date inclusion on the website.

...

Might need a cleanup / decision on the inclusion of the governance, working group pages (like, if we should link them, etc. or just remove from the "download" for now) before merging.

[snostorm]

Resolved conflicts. As per @iojs/build this worked as expected. They pushed v1.6.2 and this code generated the page updates automatically as well as updating the new releases page.

@iojs/website review?

[snostorm]

Any blockers @iojs/website ?