[issue #558] - Signal handling, zoom and light motor fix

Created by: marcus-oscarsson

Hi,

I started to look at issue #558 (closed) and issues related to it that we have observed. I discovered some issues related to the signal handling while doing this. So I took the opportunity to solve those and clean up the code a bit.

In short I tried to make the signal handling a bit more effective, when it comes to the number of signals sent and calculations made in signal handlers. It speeds things up quite alot for us, so I hope it will do the same for you.

This PR fixes issue #558 (closed)

Marcus