Define cacti system paths as constants for better code checking

[netniV]

Feature Request

Is your feature request related to a problem? Please describe

Define the paths used by Cacti as constants so that they are always available without needing $config. This also means that modifications to $config do not cause runtime issues with paths being dynamically changed incorrectly.

Also, make more paths customisable for more segmented deployments across disks.

Describe the solution you'd like

define('CACTI_PATH_CACHE',    $config['cache_path']);
define('CACTI_PATH_CLI',      $config['cli_path']);
define('CACTI_PATH_DOCS',     $config['docs_path']);
define('CACTI_PATH_FORMATS',  $config['formats_path']);
define('CACTI_PATH_IMAGES',   $config['images_path']);
define('CACTI_PATH_INCLUDE',  $config['include_path']);
define('CACTI_PATH_INSTALL',  $config['install_path']);
define('CACTI_PATH_LIBRARY',  $config['library_path']);
define('CACTI_PATH_LOCALES',  $config['locales_path']);
define('CACTI_PATH_LOG',      $config['log_path']);
define('CACTI_PATH_PLUGIN',   $config['plugin_path']);
define('CACTI_PATH_RESOURCE', $config['resource_path']);
define('CACTI_PATH_RRA',      $config['rra_path']);
define('CACTI_PATH_SCRIPTS',  $config['scripts_path']);
define('CACTI_PATH_URL',      $config['url_path']);
```