[PHP-WEBMASTER] [web-php] PR #1071: Replace MYPHPNET global var with the UserPreferences class

[MauricioFauth]

Pull Request: https://github.com/php/web-php/pull/1071
Author: MauricioFauth

- Replaces the `$MYPHPNET` global variable with static properties of the 
`phpweb\UserPreferences` class
- Moves the `MYPHPNET_URL_*` global constants to the `phpweb\UserPreferences` 
class
- Removes the `src/autoload.php` include in `shared-manual.inc` as it is 
already included in `prepend.inc`