Change "variables_order" PHP setting check to be letter-order agnostic

We recently #0000413 introduced system setting step where PHP settings are checked to ensure that In-Portal can work on a given server.

1. I've noticed that we are checking if "variables_order" setting contains "GPC" string. But what we should be checking if each of "G", "P" and "C" letters are present in that variable no matter of their order.
Also "S" letter (for $_SERVER) presence should be checked as well.

2. Then additional check must be added for "request_order" setting. If it's value not empty, then check for "GP" presence in it. If it's value is empty, then check for "GP" presence in "variables_order" instead.