Implement Engine, add compile_shader to rendering systems

- Implement the initial version of the run method of the glium platform
- Add asset manager to the context of the renderer. I will probably move that to either the engine or somewhere else later.
- Other unimportant stuff that I'm too lazy to include here. Early stage commit messages don't really matter anyways.

raidillon_glium/src/system.rs

@@ -1,16 +1,20 @@
 use std::collections::HashMap;
+use std::sync::{Arc, RwLock};
 use raidillon_core::Scene;
 use glium::Surface;
+use crate::GliumAssetManager;
 
 pub struct RenderingContext<'a, S: Surface> {
     pub scene: &'a mut Scene,
     pub target: &'a mut S,
+    pub asset_manager: Arc<RwLock<GliumAssetManager>>,
 }
 
 /// The internal "rendering system" trait of raidillon_glium.
 /// This is unrelated to the main System trait in raidillon_core.
 pub trait RenderingSystem {
     fn render<S: Surface>(ctx: &mut RenderingContext<S>);
+    fn compile_shaders() {}
 }
 
 type SystemID = String;