Made masthead and navbar partials

Same look and functionality as it was before. The only difference is that I fixed a simple typo and converted the masthead and navbar that was being used on all pages for it to be a partial instead of it being coded on every individual html page. This makes it easier to make changes to the masthead and navbar as they only exist in one place now instead of copy/pasting it manually to every single page on the site.

I will upload to s3 but just fyi so that your repository is updated and we don't break what's live right now.