Support for custom alternative cost targeting

[Eradev]

Added further support for custom cards targeting using Named$.

Now supports naming AlternativeCost

S:Mode$ AlternativeCost | Named$ Showcase | ValidSA$ Spell.Self | EffectZone$ All | Cost$ 3 U | Description$ Showcase {3}{U} (Then if you cast this for its showcase cost, create a 1/1 red Bard creature token that can't block and exile this. Whenever it attacks, you may cast a free copy of this.)

Allowing targeting like the following

T:Mode$ SpellCast | ValidActivatingPlayer$ You | ValidCard$ Card | Condition$ FromNamedAbilityShowcase | Execute$ TrigToken | TriggerDescription$ Whenever you cast a spell for its showcase cost, create a 2/2 blue Drake creature token with flying.