Minor update II - tutorial & UI

Hello. 

Recently a friend gave me quite a few feedbacks, so I took the time to implement them. 

Changes :

• Added a tutorial, to help clarify the controls & game mechanics.
• Changed main menu so it has level selection, and you can check how much shoomples you found in a level
• Changed the HUD so it's more explicit on how to switch tools
• Added prompt on pickable objects so you know what input is nescessary to pick them up.
• adjusted a ramp in level 1 so shoomples wouldn't get stuck in a corner. 
• Changed the way to leave/restart a level by making it a menu, so it can't be done by accident. 

Some good progress in my opinion.