Changed the console blank timeout

The screen blanks after a predefined timeout (during installation).
This change sets that timeout to 60 minutes, buy which time the
installation should hopefully be finished.
It is/was indeed annoying, but now that I'm using a serial console I don't look at my monitor anymore.
I've defined an online_config parameter which points to a file on my (local) server. That way I can do these kind of experiments without constantly having to build and write a new image :wink: 
At first it was only the first line, but I've extended it a bit:
```
echo "Hoi hoi from online-config.txt"
wait_in_mins=10
echo "Now we're going to wait for an arbitrary $wait_in_mins minutes to see whether the monitor stays on... "
for i in `seq wait_in_mins -1 1`; do
        sleep 60                                                                                                                                            
        echo -n "$i.. "                                                                                                                                     
done                                                                                                                                                        
echo ""                                                                                                                                                     
echo "Let's continue with the installation!"
```