Examples: Update example images with those from WP core.

[kwight]

#1106 introduced WikiMedia images with non-GPL-compatible licenses. This PR swaps them out for WordPress core's own Public Domain example images, which are all hosted on the WP.org CDN.

In WordPress/gutenberg#17493, @jasmussen also points out https://commons.wikimedia.org/wiki/Featured_Pictures_in_the_Public_Domain, giving CoBlocks other options to this PR too.

These images are all licensed under one form or another of the CC Attribution-based licenses, meaning "You must give appropriate credit, provide a link to the license, and indicate if changes were made."

• https://commons.wikimedia.org/wiki/File:St_Pancras_Railway_Station_2012-06-23.jpg
• https://commons.wikimedia.org/wiki/File:Headey,_Lena_(2007).jpg
• https://commons.wikimedia.org/wiki/File:Beautiful_river_landscape_in_the_fall.jpg (PD)
• https://commons.wikimedia.org/wiki/File:Landscape_of_Jackson_Hole,_October_2010.jpg
• https://commons.wikimedia.org/wiki/File:California_Drought_Dry_Riverbed_2009.jpg (PD)
• https://commons.wikimedia.org/wiki/File:Taiga_Landscape_in_Canada.jpg
• https://commons.wikimedia.org/wiki/File:Lesotho_Landscape.jpg
• https://commons.wikimedia.org/wiki/File:Landscape_dunes.JPG
• https://commons.wikimedia.org/wiki/File:WordPress_logo.svg
• https://commons.wikimedia.org/wiki/File:Enjoying_summer.jpg

These images were actually fine, being Public Domain:

• https://commons.wikimedia.org/wiki/File:Beautiful_river_landscape_in_the_fall.jpg
• https://commons.wikimedia.org/wiki/File:California_Drought_Dry_Riverbed_2009.jpg

Testing Instructions

• Apply this branch to a local testing install.
• Open a new post.
• Using the top toolbar inserter, enter the CoBlocks subsections and hover over the galleries, Media Card, and Author blocks.
• Verify the example images all appear fine.

[jasmussen]

An always on the table option is, of course, to take your own photos and release them as GPL V2 or Public Domain, in case the somewhat sober selection on WikiMedia is unimpressive.

[AnthonyLedesma]

@kwight Thank you for taking the time to put this request in. The images are perfectly acceptable for this iteration. Approved.

[richtabor]

Good stuff!