Bug fixes #01

• x2 and x3 combos now work as inteded.
  
• x3 green combo now discovers a random Point of Interest not yet discovered.
• Now, when a tile on the grid is destroyed, you cannot place another tile adjacent to the one that just disappeared.
• The Game Over condition now correctly triggers when you have no more placeable tiles and there are no glyphs or stairs.
• Volume and BGM buttons now work.

Bugs that are still present:

• The Game Over condition doesn't trigger when there is a glyph present that can't be clicked after the tile that revealed it has been destroyed.
• Some visual bugs regarding the tile walls.
• Very rarely you can place a tile inside a wall when left clicking between two grid cells.