Default value check is too greedy and raises issues in practice

In

Lines 1021 to 1023 in b2667b3

    
           if (languageCodes.indexOf(value.toLowerCase()) !== -1) { // language codes 
        
             return true; 
        
           }

default fields that contain one of the language codes only will be purged. This is too greedy and also hits the simple English word "No" that happens to occur in GameMap as a translatable word, cmp. https://github.com/otacke/h5p-game-map/blob/master/semantics.json#L1065

	if (languageCodes.indexOf(value.toLowerCase()) !== -1) { // language codes
	return true;
	}