WIP: rewrite of Machine overview for clarity, add diagrams
rewrite/re-organize Machine topics; incl. get started on local VM, menu order, titles
replaced Swarm info in cloud doc to reference new Swarm provisioning topic per @moxigirl, incorporated review comments per Chanwit into Concepts topic
added mention of Swarm clusters to Overview, and links to Swarm topics in What's next for Overview and Concepts
updates to concepts per @bfirsh comments
updated cloud provisioning topic to illustrated, step-by-step version added for cloud installs per issue #18282
cleanup of links, copy-edits
update to concepts, added link to boot2docker repo and re-worded per Nathan's comments
updates to concepts and cloud example per @dmp42 comments
updated for links and improved intro content for cloud topic
Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
