Add an easy-to-switch system for app.php?controller= vs mod-rewrite usage in append_sid

The current code was designed to so one can easily rewrite the controller URLs to his forum root and usw mod-rewrite to map it on the app.php

However the code does not know this, while the urls are generated. So I'd like to see an option for that in the ACP > Server settings, which then automatically changes the urls created in append_sid.

Otherwise every mod/ext author will have to implement this on his self and the admin needs to change it for every extension, or even the authors dont add code to enable this and the admin has to dive in the code again.

Patch should therefore:

• Add a config
• Rewrite the urls if they map the app.php file and include a controller argument