restore progress bar to extract DTS track

[choekstr]

Using the same mechanism that we used for ffmpeg we now have a way to bring back the progress bar for mkvextract while keeping the output clean and terse:

# Extract the DTS track
doprint
doprint $"Extract DTS file from MKV."
doprint "> mkvextract tracks \"$MKVFILE\" $DTSTRACK:\"$DTSFILE\""

dopause
if [ $EXECUTE = 1 ]; then
        color YELLOW; echo $"Extracting DTS Track: "; color OFF
        nice -n $PRIORITY mkvextract tracks "$MKVFILE" $DTSTRACK:"$DTSFILE" 2>&1>/tmp/mkvextract_output &
        PID=$!
        while [ -e /proc/$PID ];do
                echo -ne "\r$(tail -1 /tmp/mkvextract_output)" #Inject size in output
                sleep .5
        done
        checkerror $? $"Extracting DTS track failed." 1
        cleanup /tmp/mkvextract_output
        timestamp $"DTS track extracting took: "
fi

[choekstr]

Submitted a version with this to dev branch. Please test and ensure no issues

[choekstr]

Output is cleaned up and progress percentage works as expected. Closing issue.