base: fix static files serving from DocumentRoot

* Implements Nginx's "try_files" like functionality using custom wsgi
  middleware for Apache and WSGIScriptAlias for invenio.wsgi together
  with mod_rewrite.

* NOTE regenerate your apache configuration by running
  `inveniomanage apache create-config`.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Tested-by: Yoan Blanc <yoan.blanc@cern.ch>
base: wsgi middlewares reorganization

* Fixing DebbugedApplication middleware usage.

* Using an Apache environment variable to detect when to apply
  the WSGIScriptAliasFix: `WSGI_SCRIPT_ALIAS` pointing to the
  script name.

* NOTE regenerate your apache configuration by running:
  `inveniomanage apache create-config`

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reviewed-by:  Jiří Kunčar <jiri.kuncar@cern.ch>