One layout for each kind of page

There are four kinds of pages in my personal blog: home (with post
listings and a small introduction), posts, about and projects (which
will receive some love & care soon). Each one has a layout, all deriving
from `default.html`.

I'm pretty sure this is going to be helpful in the future.
Refactored html includes

Some cleaning was required, e.g.: removing bootstrap classes, old code,
improving names and avoiding more clutter. Some tabs instead of spaces
were troubling as well.