models converted to use png

All models are converted to use png  ( in techtrees case only if png was smaller)
This saves a lot of space and we don't loose anything because png is lossless
Converted all tileset and techs models to use png

This saves a lot of space and we don't loose anything
becasue png is lossless.
Techs was converted with "keepsmallest" options so png was only
used when it saved space.