update map screenshots

[drweissbrot]

Currently, the screenshots in src/themes/fennec/img/maps are from the CS:GO game files.

We should update these to CS2 screenshots.

If possible, we should include a script to extract them from the game files (via VRF) and compress them.

We may also want to handle that there's multiple screenshots now (i.e., randomly select one of them every time) -- we may also not want to do this though :D

Best case we'd also keep backwards compatibility to CS:GO, e.g. keep using the old screenshots if preferences.isCsgo is set to true; alternatively we may want to set up a separate CS:GO version of the fennec theme.