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_platform/src/platform.rs

@@ -1,5 +1,7 @@
+use raidillon_core::Engine;
+
 pub trait Platform {
     /// Initialize platform.
     fn initialize(title: String, width: u32, height: u32) -> Self;
-    fn run(self);
+    fn run(self, engine: Engine);
 }