NOTE: The right way to use ARIA's search role when inside a form is still in discussion, anyway I
changed in a way that both works AND gets validated by W3C.

More Info on:
https://github.com/w3c/wcag/issues/113

The logo role doesn't exist.

Notes:
https://awkawk.github.io/using_nav.html
http://www.w3.org/WAI/GL/wiki/Using_HTML5_nav_element#Example:The_.3Cnav.3E_element

The header tag does not need a role attribute.

In the previous pull request I had to change location of the role, but since then the master
branch removed the wrong located search role, thus making this commit an "adder" rather than a
"changer".

This will prevent VuFind from generating an empty h4 tag.

Improved the SystemStatus AJAX call to also set HTTP status codes acc…

- allows a load-balancer to verify that VuFind is available and functional.

Can be used for example to force using SOCKS 5 proxy.

The config would look like:

[Proxy]
host = localhost
port = 5000
type = socks5

Note that turning an SOCKS 5 proxy on is as easy as executing "ssh -D 5000 username@hostname"

- used for an automatic fallback to another Solr server (a replication slave or SolrCloud replica).