New secret solving logic

[ioan-chera]

There's a new branch for secret solving. Here's what's left to do:

• intelligently handle deaf guards placed to block the way: either allow exhaustive combinations if an enemy is potentially placed to block, or somehow detect if a deaf guard blocks the way and may never be encountered.
• cache the result so it's not done each time the map sets up
• run it in background so an exhaustive solution can be found in enough time