Warning, GIGANTIC COMMIT!

Replaced Keyframe subclasses with Generic Types of Keyframe and replaced all instanceof calls
Replaced implementations of Linear and Spline interpolation to interpolate any Object that extends KeyframeValue and contains at least one public double Field. I'll need this for Keyframe interpolation in CustomImageObject Transformations
Made MarkerKeyframe *no* subclass of Keyframe to avoid conflicts with PositionKeyframe in instanceof checks for Keyframe#getValue
Created KeyframeList which extends ArrayList to provide some helping functions which DRY up the ReplayHandler
Split up ReplayHandler's keyframeList into timeKeyframeList and positionKeyframeList

src/main/java/eu/crushedpixel/replaymod/interpolation/KeyframeValue.java

@@ -0,0 +1,12 @@
+package eu.crushedpixel.replaymod.interpolation;
+
+/**
+ * An abstract class that GenericSplineInterpolation can process.
+ * Subclasses simply have to declare at least one <b>public</b> double field,
+ * and the GenericSplineInterpolation will interpolate these.
+ * <br><br>
+ * It is recommended for KeyframeValue subclasses to have a @NoArgsConstructor annotation.
+ */
+public abstract class KeyframeValue {
+
+}