Property animations track (#867)

* WiP property animations system

* Use better lerp for Angle property animations.

* Fix handling of offset in sprite component.

* Allow animating some sprite layer properties.

* Allow animating some Transform properties.

Obviously not advisable for server entities, but great for client side entities!

* Improve animation property interpolation handling.

Added a "previous" mode.
Made values that cannot be sanely interpolated fall back to this mode.

* Improve some animation docs.

Robust.Client/Interfaces/GameObjects/Components/ISpriteComponent.cs

@@ -2,6 +2,7 @@
 using Robust.Client.GameObjects;
 using Robust.Client.Graphics;
 using Robust.Client.Graphics.Shaders;
+using Robust.Shared.Animations;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Interfaces.GameObjects;
 using Robust.Shared.Maths;
@@ -9,7 +10,7 @@ using Robust.Shared.Utility;
 
 namespace Robust.Client.Interfaces.GameObjects.Components
 {
-    public interface ISpriteComponent : IComponent
+    public interface ISpriteComponent : IComponent, IAnimationProperties
     {
         void FrameUpdate(float delta);
 
@@ -23,21 +24,25 @@ namespace Robust.Client.Interfaces.GameObjects.Components
         /// <summary>
         ///     A scale applied to all layers.
         /// </summary>
+        [Animatable]
         Vector2 Scale { get; set; }
 
         /// <summary>
         ///     A rotation applied to all layers.
         /// </summary>
+        [Animatable]
         Angle Rotation { get; set; }
 
         /// <summary>
         ///     Offset applied to all layers.
         /// </summary>
+        [Animatable]
         Vector2 Offset { get; set; }
 
         /// <summary>
         ///     Color to multiply all layers with.
         /// </summary>
+        [Animatable]
         Color Color { get; set; }
 
         /// <summary>