refactor @subtitle setting

I wasn't very happy with the default setting of @subtitle across pages,
but I think setting it in a before filter for every request and then
overwriting it in appropriate sections is much better than the helper
method I was using.
make placeholders for the index page

after making sections for everything I ended up removing '/'! I'm not
sure what sort of copy I'll put here yet but I wanted a placeholder so I
stopped running into 404's when clicking around.