L3P -check page revised and renamed

[Willy Tschager]

I've updated the former "L3P -check Messages" page on the PT to use the new chart we developed at the Billund Meeting. This page has been renamed to "Common Error Check Messages" and the table is sortable. For legacy purposes, the URL (https://www.ldraw.org/library/tracker/ref/l3pmsg/) will remain the same until I move the entire PT reference section (Prim Ref excluded) to the main site.

Thanks for all the work you're doing on the "boring" stuff.

w.