New attribute page_img: logos for for pages and sections

[PhilReedData]

As discussed, I have borrowed the image page attribute from RO-Crate and used a new page_img attribute for pages to show a graphic such as a logo to the side of the page title. It also shows on the section navigation cards. There is no change to the rendered HTML in either place unless the page_img attribute appears in the front-matter of a page.

More details and images are described in a Google Doc.

This has been tested on a branch of the FAIRDOM website, and in the ETT site itself. I used the following code in _config.yml to make a remote call:
remote_theme: PhilReedData/elixir-toolkit-theme@page-img-007

This is a fork from version 3.2.0. I did not mean to change the Gemfile.lock file.

To do

• Further testing on other sites.
• Tweak the image sizes for mobile viewport and particularly wide/narrow images.
• Perhaps a flag to turn the feature off in section navigation and/or pages.

Sample images

More images in the linked Google Doc above.