start prints faster (lessen wait for heating)

If starting a print it takes it's time to heat up bed and extruder, this is always true but can be cut down tremendously with a little trick.

After a print the printer cools down and on starting another print it has to heat up again completely if it's cold.

This does not occur if the printer is switched on, because then it starts heating the platform immediately.

Therefore if after a print and cool down the printer is switched off and on again, it starts to heat up even there is no print started.

If I start to slice a new object I go to the printer if it's idle, switch it off and on again and take the SD-Card to the computer.

When I come back to start the print the platform is almost heated or already heated and I can insert the card and start the printer.

The remaining time to heat the extruder is a minute or two...

(works with firmware 0.0.5, I have no reason to update :-)