[freeciv-data] techtree extension

[Zoltán Lakatos <lakatoszoltan@xxxxxxxxxx>]

Some techtree and units ruleset written to enable usage the previously sent 
images.

It is a great in Freeciv (among others), how easy to rewrite ruleset.

The only thing, that could be better, if the length of tech goal menu would be 
limited. The techs beyond letter "L" are out of display.
(If the number of techs in j step > 30, then decrease j).

thanks,
Zoli