Major amnesia revamp

Instead of forgetting maps and objects, make amnesia forget skills.
Forgetting maps and objects could be circumvented with taking notes,
or by using an external tool to remember the forgotten levels.

Forgetting skills allows the player to optionally go down another
skill path, if they trained the wrong weapon in the early game.

Amnesia still forgets spells.

As a replacement for the deja vu messages when entering a forgotten
level, those messages will now indicate a ghost with your own name
existing on the level, given only when the level is entered for
the first time.

These changes based on fiqhack, with some adjustments.

doc/fixes37.0

@@ -79,6 +79,7 @@ fix priest created inside temple wall
 fix vault guard occasionally encasing monsters in stone
 tone down scare monster by excluding humans and uniques
 lock the castle chest
+revamp amnesia to forget skills instead of objects or maps
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository