[Tilesathome] threading renderer branch "burn cpu burn"

[Rene Wunderlich]

Hi list,

news:
* merge missing #12062 "new roma proxy" (thanks Kai Krueger)
* merge 12222 "some more lowzoom fixes"
* make the lowzoom modus able to work with optimizePngTasks

and this experimental thing:
add threading support for lowzoom file download


i hope the lowzoom thing work ;)
we sold more predownloading now


René