Custom rule severities.

ADDED severity token to custom rule syntax.  Each rule can now define
its own severity.

Fixes https://gitlab.com/kicad/code/kicad/issues/6148

pcbnew/python/scripting/pcbnew_scripting_helpers.cpp

@@ -517,7 +517,7 @@ bool WriteDRCReport( BOARD* aBoard, const wxString& aFileName, EDA_UNITS aUnits,
 
     for( const std::shared_ptr<DRC_ITEM>& item : violations )
     {
-        SEVERITY severity = bds.GetSeverity( item->GetErrorCode() );
+        SEVERITY severity = item->GetParent()->GetSeverity();
         fprintf( fp, "%s", TO_UTF8( item->ShowReport( aUnits, severity, itemMap ) ) );
     }