Merge all Xerces rules into one rule

Indeed for the time being there is one rule for each kind of error reported by Xerces but this approach has several disadvantages :

• Rule names are meaningful as they duplicate the xerces violation messages. Example :

Element ''{0}'' cannot have character [children], because the type''s content type is element-only

• Most of the time you don't need and don't wan't to activate each kind of possible violation independently

So the solution is to group all those violations behind the same generic rules.