Bug 997577 - Consolidate legal pages in new /about/legal hub

[Bug 997577](https://bugzilla.mozilla.org/show_bug.cgi?id=997577)

Legal pages are consolidated under a new /about/legal/ hub. This PR sets up the new /about/legal/ page, 

Some new pages have been added, some have been moved to be imported from the mozilla/legal-docs repo, and some are links to external sites. Redirects have been added where URLs have changed. This spreadsheet shows which pages/URLs have changed: https://docs.google.com/a/silverorange.com/spreadsheets/d/1HAq3CAnvora4HS8rWtzFgw0cjBgHMJpMXfQH3FjRYoE/edit#gid=0

The requirements from the bug are listed in https://docs.google.com/a/silverorange.com/document/d/1GTmEOv8s4NfOLs_DNk5X01FGr2cr_qjW0u1V9uMhxX8/edit

This PR is ready for code review, but please do not merge, as we are still waiting on content review from Legal.
<code>hgroup</code> was axed from the HTML spec, we should probably avoid using it and try to remove existing appearances. This could be a <code>header</code> or <code>div</code> or, in this case, maybe even the bare <code>h1</code>.