Support for full NES2.0 headers

[tjanas]

Nt Mini JB will refuse to load any NES rom file that has the last two bytes of the header (byte 0x14 and byte 0x15) set. These two bytes need to be zeroed out to allow the Nt Mini Legacy to load the rom, making it not possible to share a common and correct NES2.0 set of roms.