Use sublayout for post.html to remove includes

By giving _layouts/post.html a header, it becomes a sub layout whose
content is placed in the parent's {{ content }} block. This prevents
duplicating the {% include header.html %}, etc. calls between different
layouts and makes viewing the whole <html> body in default.html easier.
Remove duplicate <meta> tags

* X-UA-Compatible was defined twice. Prefer the version with no
  self-closing slash since HTML5 does not require it.
* Content-Type is covered by the <meta charset> tag above and is not
  needed.
Remove class on click to prevent lingering hover effect

The CSS :hover selector requires a mouseleave/mouseout to remove its
effect, and because of the sliding top bar the mouseleave doesn't
happen on touch devices.

By adding and removing a "hover" class name, the JS can remove the
"hover" on click as well to prevent having to wait for a mouse out.

Fixes #7.
Merge pull request #11 from ssorallen/mobile-hover

Remove class on click to prevent lingering hover effect
Merge pull request #12 from ssorallen/layout-unification

Layout unification