Replace nvbw images with CC0 images

[wielandb]

This PR will replace all images in the directory /dependencies/nvbw_open_data/images with images that I took myself and put under the CC0 license.

[wielandb]

At this point, 18 images remain to be replaced.

[wielandb]

At this point, 17 images remain to be replaced

[wielandb]

At this point, 4 images remain to be replaced.

[wielandb]

• [ ] Ensure minimal resolution of 1000x1000 and a maximal resolution of 2000x2000

At the moment, the following images violate this rule:

• [x] approach_aid_no.jpg (too big!)
• [x] automatic_door_button.jpg (too big!)
• [x] disabled_parking_1.jpg (too small!)
• [x] disabled_parking_2.jpg (too small!)
• [x] disabled_parking_3.jpg (too small!)
• [x] handrail_2.jpg (too small!)
• [x] handrail_tactile_writing_1.jpg (too big!)
• [x] handrail_tactile_writing_2.jpg (too big!)
• [x] kerb_flush.jpg (too big!)

[7h30n3]

The only two things missing are a new image for streetside parking and checking if all images are numbered correctly.

[wielandb]

Should be ready for final review now. :)