* fix(backend): add compatibility with centreon 18.10

* manage other compatibility issues

* fix coding style

* Update www/modules/centreon-nagvis/nagvis-config.php

Co-Authored-By: kduret <duret.kevin@gmail.com>

Add simple but very useful refresh button.

Mix img path in doc

Doc update + fix missing upgrade path

Mostly code cleanups

Implements prefs, should be working now

Purge old unused *.tpl files
Start merging code from contributor