Fix a bunch of HTML5 validation errors.

- For some reason, the W3C validator complains about the self-closing
  tag <i class="icon-ok"/>, but we write it as <i class="icon-ok"></i>.
  I tried to fix it by inserting an &nbsp.
- We need to escape & in URLs, so I just run the entire S3 URL through
  an HTML escaper.
- Changed a <span> to a <div>, since we can't nest <div>s inside
  <span>s.
- <th> tag can't use the width attribute, so I switched it to using CSS
Move styles to an external stylesheet
Upgrade to jQuery 2

We still keep jQuery 1.9 around with conditional comments, so can
support IE 6/7/8. But it still accomplishes the goal of reducing page
load time for modern browsers, since jQuery 2 is smaller.
Merge pull request #42 from TeamAmalgam/fix-html-validation

Fixes #5 (HTML validation), #4 (jQuery 2), and factors CSS out to external stylesheet