Restructure the Ubuntu Getting Started Section.

- This supercedes PR #1770
 - This breaks up the section from one huge installation page into:
   - A new index page.
   - New support grid with commercial and community support options.
   - Move to lifecycle-based pages based on operational tasks.
     - Add support for local deployments via LXD.
       - Added screenshots to images/docs/ubuntu
     - Add backup page.
     - Add decommissioning page.
     - Add a glossary of terms page.
     - Rewritten installation page.
     - Add logging page.
     - Add monitoring page.
     - Add networking page, flannel only for now, calico in progress.
     - Add a scaling page.
     - Add a security page.
     - Add a storage page.
     - Add a troubleshooting page.
     - Add an upgrade page.
     - Add a cluster validation page.
     - Add new ubuntu content to the index page.
       - Add Ubuntu to _data TOC.
     - Add warning about choosing ipv6 with LXD, thanks Ed Baluf.
     - Template-ize all the pages per jaredb's review.

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