wip: Changes of the week

- Move engine to a different crate
- Add engine trait
- Refactor the rest of the codebase to work with these changes
- Add debug ui buffer, use it to finish imgui support

core/src/system.rs

@@ -1,38 +0,0 @@
-use crate::Scene;
-use indexmap::IndexMap;
-use winit::event::Event;
-use crate::context::PlatformContext;
-
-pub struct SystemContext<'a> {
-    // TODO: time delta etc.
-    pub scene: &'a mut Scene,
-    pub platform_context: PlatformContext,
-}
-
-pub trait System {
-    /// Initialize the system.
-    fn initialize(&mut self);
-    /// Spawn the first entities of the world.
-    fn load_world(&mut self, ctx: &mut SystemContext);
-    fn update(&mut self, ctx: &mut SystemContext);
-}
-
-pub type SystemID = &'static str;
-pub struct SystemManager {
-    pub systems: IndexMap<SystemID, Box<dyn System>>,
-}
-
-impl SystemManager {
-    pub fn new() -> Self {
-        let systems = IndexMap::default();
-        Self { systems }
-    }
-
-    pub fn add_system(&mut self, id: SystemID, system: Box<dyn System>) {
-        self.systems.insert(id, system);
-    }
-
-    pub fn remove_system(&mut self, id: SystemID) {
-        self.systems.shift_remove(&id);
-    }
-}