Added images, columns, and css rules

Added images to img folder. Added id “intro” in index.html and added
width, height, background image, and background size rules in base.css.
Added classes for columns. Added class for row. Added row height rule
in css. Added sticky nav bar. (Got the html from foundation docs).
Added title block into intro. Added padding, border, margin-top,
text-align, color, font-size, text-transform, and letter spacing rules
to .title-block in base.css