New design

Had a go at re-designing the site. 

@jonmagic It needs tweaking with a real lesson in there and for registration (registration or full lesson info won't show locally). Either ping me on how to do that or see if you can work with my css. Also need email link for people who want to be mentors.

Content also needs reviewing - anyone can chip in on that if they have ideas, I just made a start. I put in a ying yang logo thing on there, not sure if we need that but it seems to kinda be the logo on the other sites, and that was the least bad version of it I could think of.

@kneath let me know if it's okay to use your photo in the banner. That one just works nicely :)

/cc @CoderDojoSF/mentors