Refactoring, reorganization and cleanup (#7)

### New `math` module
 * Traits for error-tolerant floating-point comparisons
 * Traits for interpolation and easing
 * Bevy plugin to manage 3D interpolations with ECS components

### `skybox` module refactor
 * ECS resource to enable external skybox selection/updates
 * System run conditions for more idiomatic/ECS-friendly control flow

### Camera controller refactor
 * Renamed from `orbit_cam` to `camera_controller`
 * Now delegates to the new interpolation plugin for WASD motion smoothing
 * Simple API for attaching the `CameraController` component to the camera from
   another module -- this resolves an awkward separation-of-concerns situation
	where we had to configure a bunch of render-quality settings in the camera
	controller module

### Scene module refactor
 * Renamed from `test_scene` to `scene`
 * This module is now responsible for configuring the skybox
 * This module is now responsible for spawning the camera and configuring the
   render settings

studio/src/math/mod.rs

@@ -0,0 +1,6 @@
+mod float_comparison;
+mod internal;
+pub mod interp;
+
+pub use float_comparison::*;
+pub use interp::*;