Implement player maze-building

[vlbeaudoin]

Player should be able to build and deconstruct certain tiles in the tower zone, in order to build a maze of fences and towers on top of those mazes, which they should then be able to operate (only allow chickens to fire at mobs if they are currently manning any tower)

[vlbeaudoin]

• Figure out if the player can build only between waves or during them as well.
• Prevent adding a building that would block the path from the start to the destination

[vlbeaudoin]

The simplest would be to not allow the creation of walls during waves, only between. Towers, however, could be built whenever.

So the path would be calculated only once, as the wave starts.