Added boat trails to the boat group, fixed annotations

- Set colours for the annotations
- Added boat trails back into the boat group
- Re-added time until next mark and time since last mark rounding

#story[923]

src/main/java/seng302/models/Yacht.java

@@ -151,7 +151,7 @@ public class Yacht {
         this.colour = colour;
     }
 
-    public double getVelocity() {
+    public Double getVelocity() {
         return velocity;
     }