Clean up HTML/CSS.

- Move CSS to external file (even though it's tiny, just so they
  get more exposure to CSS-as-external-file, which is the common
  practice

- Use more idiomatic Bootstrap-isms for presenting the messages
  (as listitems, rather than paragraphs)

- Remove Bootstrap navbar, wasn't being used

- Minor HTML cleanups (text attrib not allowed on textarea, etc)

- Strip the textarea (bug exposed when textarea tag breaks, but,
  really, we should consider any all-blank message as blank, not
  just "")
Merge branch 'master' of https://github.com/hackbrightacademy/Javascript3