Dianne Tennent authored Jul 25, 2022 and Robert Lyon committed Oct 12, 2022

* Description in the context of images is now called 'Caption'
  in the frontend
* Images now have an 'Alttext' field,
  e.g. for non-displayed assistive technologies.

* Hierarchy :
1. altiscaption is true, then alttext (whether empty or not)
2. altiscaption is false and caption is not empty, then caption
3. altiscaption is false and caption is empty, then title

- add 3 new columns to artefact_file_image table
- ability to save bool for if image is purely decorative
- saves alt text
- saves bool for if alt = caption
- for linked images, the <A> tag wraps around the image and the
caption, so that if the alt text is empty (when
description is same as alt), the link has a label for
screen readers
- added <figure> and <figcaption> when 'showdescription' is on
- deleted thumbnails.tpl as it is not being used anymore
- tidied up square thumbs so that caption will avoid being cut off
- add help text for isdecorative, alttext, and
altiscaption fields
- added a 'show caption' to image formatting options' when adding
image via TinyMCE so that it can have a caption

Change-Id: I80c2d62e45bb08d59b6f8d3033a113fcd30ae9a7