Added generic typing to layer properties and keyframes

Restructured the way property input VMs are created

src/Artemis.Core/Models/Profile/LayerProperties/BaseKeyframe.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace Artemis.Core.Models.Profile.LayerProperties
+{
+    public class BaseKeyframe
+    {
+        protected BaseKeyframe(Layer layer, BaseLayerProperty property)
+        {
+            Layer = layer;
+            BaseProperty = property;
+        }
+
+        public Layer Layer { get; set; }
+        public TimeSpan Position { get; set; }
+
+        protected BaseLayerProperty BaseProperty { get; }
+        protected object BaseValue { get; set; }
+    }
+}