Table on Sandbox.WebHome is missing the header

AFFECTS:

• xwiki:Sandbox.WebHome (en, ca, da, de, es, fr, it, lv, pt_BR, ru, zh_TW, zh)

ERROR:

• org.xwiki.test.webstandards.CustomDutchWebGuidelinesValidationTest.Validating HTML5 Dutch Web Guidelines validity for: xwiki:Sandbox.WebHome {pt_BR}

  executed with credentials Admin:admin (from org.xwiki.test.webstandards.AllTests)

• ERROR: At least one table has been found that uses no th element.

INVALIDATES:

• Dutch Guidelines: {{validateRpd11s2() }}
  • https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-tools/xwiki-platform-tool-standards-validator/src/main/java/org/xwiki/validator/DutchWebGuidelinesValidator.java#L1065
• R-pd.11.2 "Use the th (table header) to describe a column or row in a table with relational information."

EXPLANATION:

• Data tables should contain a header
  Tables which contain data (as opposed to layout tables) should contain proper table header elements to mark them for screen readers and enhance the structure of the document.
• The problem with this issue is that it's not a bug. The example showcase how a table looks like without a table header.

FIXES:

• VAR1: Add a hidden th for the table
• VAR2: Add an exception for this case in https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-distribution/xwiki-platform-distribution-flavor/xwiki-platform-distribution-flavor-test/xwiki-platform-distribution-flavor-test-webstandards/src/test/it/org/xwiki/test/webstandards/CustomDutchWebGuidelinesValidator.java since the behaviour is intentional