blackbox_encode process all flights in a log

[bizmar]

blackbox_encode requires the user to specify a log which makes automation more difficult, my request is:

1. If no --index is specified, process all flights
   or
2. allow for -- Index ALL or 0 that processes all logs

[bw1129]

is this feature related to the fact that if there are > ~30 logfiles, bb_decode only converts the first ~30? the reason I ask is because for some reasons, some onboard logging devices seem to be recording a bunch of empty logs.