[TCOTD2] fade out key map markers that have already been unlocked

[nashmuhandes]

Just a way to tell the player what they (or have not) achieved

[nashmuhandes]

Addressed with https://github.com/Realm667/Re-Releases/commit/012dd56fb4a507347620309b47eede6994e86a67

(map marker alpha cannot be modified, so what I did instead was add scripted checkmark spawns)