Replace function PMA_performConfigChecks by a class.

Hi,

I replaced the PMA_performConfigChecks by a class.
This is the first class that I create in pMA. Is it ok for you? Is it well named and in the good folder ?
Shoud I add the prefix "PMA_" ?

I added a little change: the configuration isn't get from $GLOBALS in the method, but is given by the caller.

Any comment about this work ?

Thanks,
Hugues.