Improvements to base.html
Improvements to base.html

- Use `url_for` function for links to static assets
- Remove Google Analytics snippet, which is no longer needed
- Update to latest recruiting comment at the top
- Update path to html5shiv based on changes to its repo
- Minor formatting cleanup

Scotchester/cfgov-sheer-templates,Scotchester/cfgov-sheer-templates,cfpb/cfgov-sheer-templates,cfpb/cfgov-sheer-templates