Implement more file system related error checking and reporting

[mrehkopf]

Some error conditions, such as "card full" and "file not found" errors are not handled gracefully and are not reported to the user. This can result in unsaved games without the user noticing.

[mrehkopf]

This is implemented now as LED blink codes during gameplay. The issue remains open because there are no warnings issued by the menu before running the game, and there is a lack warnings for missing supplemental files such as DSP roms.