base: adaptation to new search form from invenio

This is needed to adapt code to this commit at invenio side:

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>

https://github.com/jirikuncar/invenio/commit/2312dee28cdcfc7de709071dd31f71e658b3eac8