[altsys] checking of HTML editor installed

Other modules can be checking HTML editor installed.

ex.
```php
if (defined('XOOPS_CUBE_LEGACY')) {
	@ include_once XOOPS_TRUST_PATH .
'/libs/altsys/class/altsysUtils.class.php';
	if (XC_CLASS_EXISTS('altsysUtils') &&
is_callable('altsysUtils::isInstalledXclHtmleditor')) {
		if (altsysUtils::isInstalledXclHtmleditor()) {
			// case of installed HTML Editor
		} else {
			// case of NOT installed HTML Editor
		}
	}
}
```