Shorten Dashdash post, replace iPhone w/ Lifeline

Note the new top-level "other" folder for things that should be in version control, but that aren't part of the blog itself.
Minor edits, including improved video embed size
Incorporate fantastic suggestions from @kvanscha – thanks!

Google doc with comments/suggestions: https://docs.google.com/document/d/1iunW3pqVZ0zZSZgBygtNYUNQHUpEhmuRIP2w1Wiqh_8/edit
Clean up Lifeline Excercise diagram