Continue new platform/glium implementations

- Assets, asset manager system
- Rendering system trait
- Kick off glium platform implementation
- And more

raidillon_platform/src/context.rs

@@ -1,11 +1,7 @@
 use winit::event::Event;
 use crate::AssetManager;
 
-pub struct FrameContext {
-    pub event: Event<()>,
-}
-
-pub struct PlatformContext {
-    pub frame_context: FrameContext,
-    pub asset_manager: dyn AssetManager,
+pub struct PlatformContext<AM: AssetManager> {
+    pub current_event: Event<()>,
+    pub asset_manager: AM,
 }