[core] allow detection and format of "raw" drives

* eg. GPT drives with no partitions were not enumerated by default
* fixed disk mode needs to be enabled for this detection to occur
* also fix the unwanted use of a drive letter in GetDrivePartitionData
* also add a check for going over MAX_DRIVES
* also fix improper separator line in FreeDOS menu due to UTF-8 source
* closes #124