Open directory as disc

Allows to run a game that was extracted to a folder. Use "File->Open directory" and point it to the folder that contains PSP_GAME.
I extended the DirectoryFileSystem class for this. Block numbers for sce_lbn are assigned on the fly, every time FileInfo is called on a new file it reserves the necessary number of blocks for it.

It doesn't work with games that open the entire ISO as a file, for example SRW Masou Kishin 1. If there are games that use sce_lbn without using the block number returned by file info as a base, then those also won't work.

Maybe something can be done about those games later on? I'm not sure.

It would be nice if someone could test it a bit more before merging. It worked fine with my other games, but you never know.