Custom filenames with autoscreenshot

[gak]

Suggested by Emanuel Larsson:

First I would likte to be able to save the simulation and a snapshoot image of it with. This can allready be done but you have to name the file. I would like it to be named automatically if left out (alternatively a different command) with something like a date/time stamp name (eg: "yy-mm-dd_hh-mm.bmp"). Then this command could be excecuted from the timer function even in screensaver mode.

[FrMo]

soution could be done together with issue #49 (use spawn name as default simulation name)