upgraded validation for playsets to an error
upgraded validation for playsets to an error

Exceeding 4 of a card across main/side should be an error instead of a warning.
Added note to abstract the error level used for constructing notifications.

ideocl4st/decklist,Fryboy/decklist,marumari/decklist,marumari/decklist,ideocl4st/decklist,Fryyyyy/decklist,ideocl4st/decklist,Fryboy/decklist,Fryyyyy/decklist,marumari/decklist,Fryyyyy/decklist,Nightfirecat/decklist,Fryyyyy/decklist,Fryyyyy/decklist,marumari/decklist,Fryboy/decklist,Fryboy/decklist,Nightfirecat/decklist,ideocl4st/decklist,Nightfirecat/decklist,Nightfirecat/decklist