webui: display sysnames/hostnames instead of ip addresses #4155

When a network is mostly assigned using RFC 1918, DNS resolution is not useful
and devices are displayed by IP address.

When $config['force_ip_to_sysname'] is enabled, use ip_to_sysname() to display
the device hostname or SNMP sysName if present instead of the device IP address.

UI modified by this patch:
- Hover in Dashboard Availability Map (/overview)
- Name in Availability Map (/availability-map/)
- Title of device page (/device/device=...)

* I agree to the conditions of the Contributor Agreement contained in
doc/General/Contributing.md.

GitHub-issue: #4155
Suggested-by: Andres Rahn <andreser@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

AUTHORS.md

@@ -152,6 +152,7 @@ LibreNMS contributors:
 - Markus Wigge <markus@cultcom.de> (cultcom)
 - Matthew Wall <llawwehttam@gmail.com> (llawwehttam)
 - Andres Rahn <andreser@gmail.com> (Andreser)
+- Philippe Mathieu-Daudé <philmd@users.noreply.github.com> (philmd)
 - Christoph Zilian <czilian@hotmail.com> (czilian)
 - Guillem Mateos <bbguillem@gmail.com> (guillemmateos)
 - Joachim Tingvold <joachim@tingvold.com> (jallakim)