base: footer modularity improvement

* Removing styles on the <footer>. It's a generic element that may be
  used at more than one place, like <p> or <address>.
  http://www.whatwg.org/specs/web-apps/current-work/#the-footer-element

* Adding blocks in the footer template so one can reuse the content
  without having to keep the outter structure.

* Removing inline style.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
search: search form as files

* Splitting the `search_form` macro into files. All the blocks have been
  preserved.

* Deleting the `search_form` macro.

* NOTE if you were using the `search_form` macro you should replace it
  by `{% include "search/form/index.html %}`

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>