fix opendir bug for multiple FAT volumes
Add sd card insertion detection and mount exernal sd
fix a bug in readdir that casued stack overrun (fixed in upstream mbed already)
move extern sdcard detect to panel
allow configure of where extern sdcard is plugged in
when extern sdcard is inserted jump to that directory in play screen
switch SDCard to use mbed::SPI as it remembers the frequency to use for each device
fix white space changes
update pins for viki2 on an azteeg X5 mini V2
Merge pull request #518 from wolfmanjm/add/external-sdcard

Add/external sdcard