Fix broken preset images, add local images

[tordans]

The traffic sign presets are broken ATM. It looks like the files where removed from Wikipedia?

I took some images from https://github.com/zlant/parking-lanes/issues/69 and added them to the repo. Also two from Wikipedia.

There are also some images for Australia https://github.com/zlant/parking-lanes/pull/44 already in the folders (FYI @jakecoppinger).

TODO

• [ ] Find a place to attribute the images; find out hot to attributes them; add attribution.
  • Suggestion: We could maybe add all attributions to the /src/assets/README.md and add a link to there from the details panel (bottom right).

Changes

• add images from Wikipedia and StreetComplete
• configure Webpack to serve images (and rename plugin for consistency)
• fix and add Russian signs

[tordans]

I should also post an 'after' screenshot, right? :-)

[tordans]

TODO: This does not work with the build step, yet. Will look into it…