Add progress to Muxing portion

[choekstr]

Using the same technique as ffmpeg to grab just the progress bar I have reworked the Muxing portion to add progress updates in realtime.

Here is the code that needs replacing:

        if [ $EXECUTE = 1 ]; then
                color YELLOW; echo $"Muxing AC3 Track in:"; color OFF
                eval $CMD >/tmp/mkvmerge_output &
                PID=$!
                while [ -e /proc/$PID ];do
                        echo -ne "\r$(tail -1 /tmp/mkvmerge_output|grep Progress)" #Display progress from outp
ut
                        sleep .5
                done
                checkerror $? $"Merging the AC3 track back into the MKV failed." 1
                cleanup /tmp/mkvmerge_output

        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.