Fix: present spawning

The ZIP containing the sources is now updated.

The presents now won't spawn on top of another one. This is simply achieved by using a list of free spaces (free cells from the tilemap).

It is first initialized with the cells from the tilemap that we consider free. Then, each time a present is spawned or is collected by the player, the list of free cells is updated accordingly.

The code to calculate the free cells was called each time we wanted to get them. Manipulating an array some times in this case.

This was unnecessary. Now the cells from the tilemap are fetched once at the beginning. Then we update the array by adding or removing elements, and the call to the tilemap method to get the cells from their ID is not used anymore during the processing.

Features to be fixed or added:

• the presents spawns should not overlap, as for now multiple presents can be at the same location -> DONE
• there should be a drawback to gather a maximum of presents and wait until the very end to open them - some ideas:
  • some presents can be empty, they can have a slightly different color palette and/or design and:
    • stagger the player for some seconds
    • remove some seconds from the PlayTimer without hindering the player, or only for a split second
  • there are some traps spawned at the beginning all over the level and if the player touch them they are stopped for some time
  • simply increase the time needed to open the presents depending on the number held (can be linear or worse) -> DONE as there is now a factor that increases the more presents you are holding at once. So the more presents you have with you, the more time each present will add to the opening time
• make the screen cleaner and clearer for the player
  • improve UI placement and design
  • improve tileset
  • improve progress bar
  • improve sprites
• add FXs
• add SFXs
• find a better solution for key configuration - switching between azerty, qwerty, and qwertz is a pain - so maybe use the arrows first for movement and then maybe add the possibility to change the settings -> DONE by automatically detect AZERTY or QWERTY keyboard and reassigning the keys & also added the arrow keys by default