Add quick replay mode

Allows very quick forwards and backwards jumping at the cost of only
replaying entity positions and block updates.

Still needs to be backported from 1.12.2 and contains FIXMEs

src/main/java/com/replaymod/replay/gui/overlay/GuiReplayOverlay.java

@@ -128,7 +128,7 @@ public class GuiReplayOverlay extends AbstractGuiOverlay<GuiReplayOverlay> {
             public void run(int time) {
                 replayHandler.doJump(time, true);
             }
-        }).setLength(replayHandler.getReplaySender().replayLength());
+        }).setLength(replayHandler.getReplayDuration());
     }
 
     public double getSpeedSliderValue() {