PSF Loader improved & issue #126 fixed

* Improved PSF Loader: Now you can get the value of the PARAM.SFO
entries directly with the GetString(key), GetInteger(key) methods.
GameInfo related lines were removed since they have nothing to do with
PSF files.
* cellGame, cellSysutil, and GameViewer are modified because of the PSF
Loader changes.
* Removed unnecessary null pointer checks:
https://github.com/DHrpcs3/rpcs3/issues/126