Merge: Intro Tinks! 3D: A gamnit game with particles effects

Merge: Intro Tinks! 3D: A gamnit game with particles effects

Intro a 3D client for Tinks! built with _gamnit depth_. It uses the same logic as the 2D client so they are compatible for multiplayer games.

To support this client there was a few fix to gamnit and some new features, most notably:

* A customizable particle system with two implementations, one for smoke and one for explosions. This module is a first draft, a few features are lacking.

* The method `show_splash_screen` which displays a single texture centered on a cleared screen (by default black).This method should usually be called before loading textures and models and doing other slow work.

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Sorry for the scary diff (once again) but there is actually little code added. The main commits are the intro of the particle system and of the new Tinks! client.

Pull-Request: #1928
Reviewed-by: Jean Privat <jean@pryen.org>