"Cast as though it had flash" effects need to be reworked

If there are several effects that would allow a player to cast a spell as though it had flash, xmage should give the player a choice of which one to use, and cards should be able to distinguish which one was chosen. For example, if you have a [[Vedalken Orrery]] on the battlefield and an [[Armor of Thorns]] in hand, you should be able cast the Armor at instant speed using the Orrery's ability rather than the Armor's own ability and not have to sacrifice the Amor at the end of your turn.

Relatedly, if you cast Armor of Thorns via an effect that tells you to cast a spell (such as cascade or [[Chandra, Torch of Defiance]]'s first loyalty ability) it is incorrectly treated like casting it with its as-though-flash ability, meaning you will have to sacrifice it.