In the dropdown of the accessibility checker, replace the "WCAG2A"/"WCAG2AA"/"WCAG2AAA" with "WCAG 2.1 A(A)(A)" labels

[bdeclerc]

There appears to be confusion with users regarding the WCAG version supported by our tool - can we explicitly label the different options "WCAG 2.1 A/AA/AAA" in the dropdown in the tool's UI?

I've coded a solution into the "wcagshort" branch, this adds a "shortdescription" to the rulesets and used that to fill in the option name (leaving the option value as is)

If this is Ok, can we merge into master?

[rutiolma]

This seems ok, just added an extra validation for the shortdescription field