Use different icons for "Step" toolbar icons.

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Look for some icons here,
http://tango.freedesktop.org/Tango_Icon_Gallery

There are some excellent icons in the nemiver package.
I am attaching step-over, step-out and step-into as they are small and will save someone hunting for them.
If we continue to the existing icons then I'm in favour of a reassignment as I find the current selection is far obvious to me.
Step-into should be down rather than right.
Step-over should be right rather than up.
Step-out should be up rather than left.

I was going to do make a patch for this but realised that I need to know more about gtk-icon-factory and friends first.
The xpm files will need to reside in a system shared data folder very likely /usr[/local]/share/gnusim8085/.

OK I've learnt a bit about GtkIkonFactory.

Attached is a unified diff patch against 1.3.7 which implements nemiver/code blocks style debugger control
toll bar icons.