Remote Debugging refresh

Restructured remote debugging article and updated procedures/screenshots.

Preview:
https://rawgit.com/heatheramahan/devtools-docs/master/docs/_preview.html?remote-debugging.html 

@paulirish @Garbee @umaar @jaredwilli 

Note: This update includes minor changes to the remote-debugging-legacy doc (new images only).
Might leave a note here about canary/devchan to avoid that issue.