Wrap online tools list items in UL
Add video talks related to accessibility
update references to Bootstrap

Bootstrap is no longer organizationally affiliated with Twitter
Bootstrap's website URLs have changed
Also fixes some typos I came across
Merge branch 'patch-1' of github.com:cvrebert/a11yproject.com into cvrebert-patch-1

* 'patch-1' of github.com:cvrebert/a11yproject.com:
  update references to Bootstrap