Disappearing walls should be treated as entities rather than tiles

[vtereshkov]

I expect that all interactive elements be represented by entities with some specific tags. However, disappearing walls are treated as tiles, despite the fact that they are quite similar to doors (which are still entities).

If this is a special case, the editor API should provide a mechanism to define interactive tiles. For now, the connection between the levers and this particular kind of tiles is a total mystery.