Add BFSv1 (ByteFrost Filesystem version 1) config file support to SD Card Arduino

[ron-keidar]

Task Description: The ByteFrost Filesystem version 1 specifies that the used SD card should use the FAT16/32 filesystem and contain the following files:

SD_card/
    {ByteFrost disk file(s)} 
        #    can have more than one
    bf.con
        #    file that contains only the name of used bytefrost disk file

The bf.con file is used to allow the SD card to contain multiple ByteFrost disk files (for ease-of-use). At present, this feature is ignored by the SD Card Arduino - it only looks for a ByteFrost disk file called "disk" and if this is not found, it breaks.

Task details:

1. Add support for the bf.con file in the SD card Arduino.
2. Clean the SD card Arduino code.