Changes to hero, home_landing_row, and footer that will allow it to display info from _config.yml

Replaced hero.html content with `site.title` and `site.subtitle`. In footer.html, email icon now made dependent on `site.email`. In home_land_row.html, I added `site.description` under "about me" and made all 3 icons dependent on site configs.

These changes should make it easy for first time users of this theme to see all of the _config.yml settings immediately displayed.