Note using the "yyyy-MM-dd HH:mm" format so it is readable
for users. However, the colon, ":", is not a valid
FAT32 filename character. So when saving to the SD card,
the filename becomes "yyyy-MM-dd HH_mm".
In StringsUtils, add formatDateTime, formatTime, formatElapsedTime.
Note that verified when sending to Google Docs, no longer need
to always show the hours when displaying total time and moving time.