Removed useless iframe property

Changed the iframe so that it has some vertical padding, and also
removed the frameborder property, because it apparently wasn't valid
HTML5 and was causing a validation error.
Made website responsive

Turns out that the only thing you have to do to get a website working
responsively is wrap everything in the container div.  That's all.
It's awesome, and works for pretty much all screen sizes.  My huge
screen, a smaller tablet, and mobile all scale very well, and there is
no problem browsing in any way.
Made image responsive

Changed the image in the about us page, so that is centered as before,
but instead uses offset columns and also is a member of the
responsive-image class. This way, when the page scales down, it takes
up the entire width of the page, so it's not hard to see on a phone or
tablet.
Made iframe responsive

The embedded YouTube video now actually will scale properly just like
the image. The same technique was applied, but it was a bit more
finicky and took some work to get it to behave properly.