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>
assets: less flavor of bootstrap

* Installing less and grunt-contrib-less.

* Adding the filters parameter on the assets.
  `{% css "foo.css", "00-bundle", "less" %}`

* Adding some configuration keys.
  LESS_BIN which must be pointing to lessc.
  CLEANCSS_BIN ditto for CleanCSS
  LESS_RUN_IN_DEBUG (default True) to enable or disable the less
  bundling in DEBUG. ASSETS_DEBUG must be also set to True for
  it to work.

* Renamed base.css to base.less and it includes the less files from
  Bootstrap and Font-Awesome.

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