correct html syntax errors and remove inline css

This PR is to correct html validation issues with the following areas:
* The header menu - invalid nesting of anchor and center tags
* The container div is not closed on event template
* Duplicate use of "header" id (event template, although this exists elsewhere)

I tested in Chrome and Firefox on both a Mac and PC, in Chrome on Ubuntu, and in IE11 on Windows7.  The W3C [syntax checker](http://validator.w3.org/check?uri=devopsdays.org) will still show errors, but it should show many fewer. A page like Chicago's should be free from errors after this change.  :smiley: