Fixes #14038.

Research supporting this choice of approach:
    https://gist.github.com/cvrebert/68659d0333a578d75372

Why not <button>?
Even with a `tabindex` attribute, they don't gain focus when clicked upon in:
    * Mac OS X Firefox 30.0
    * Mac OS X Safari 7.0.5

[skip sauce] [skip validator]

.bs-docs-navbar class doesn't seem to be used anywhere at all

Also use the official filenames.

Closes #13379.

- Implements new format "Copyright 2011-xxxx Twitter, Inc.", which resonates well with our History page and more accurately reflects the copyright status of the repo
- grunt dist to update all the files