Replace header images and use gender-neutral core header text

This replaces the header images with styled HTML, removes unused header images and removes the first "made men" sentence in the core team header. This PR will fix #14.

There remains some style tweaking to be done here before it can be merged, but after a replacement font is chosen. @fxn determined that the font used in the images is Interstate, and the Blue Highway web font seems to be a very close replacement (with the exception of that apostrophe :smile:) as can be seen here (current page on top, font preview below):
![screenshot 2014-09-08 22 29 21](https://cloud.githubusercontent.com/assets/594059/4196745/fe2677ac-37da-11e4-8dfe-a583fdeb9ded.png)

The good news is that this particular font is also available for free from [MyFonts](https://www.myfonts.com/fonts/larabie/blue-highway-2/), with an unlimited page view count and only requires "purchase" once so there shouldn't be any overhead of someone updating the license each year. This seems like a reasonable solution to me instead of trying to find the best standard web font to replace it, but let me know if this has to go in another direction.

I also noticed that in a previous commit a `|` (pipe) character was removed from the navigation include so I put that back in a840401 at the risk of cluttering this PR.

Looking forward to your feedback!