Bucket objects have a value.
Give each Bucket its value when created.
Getter for Bucket value.
Let the Line keep track of number of Bucket objects stuck to it.
Increase the recorded number of Bucket objects on the Line as they stick
to the line.
Store every bucket added to the line in the Line object.
Buckets only stick if they are in the correct order.
Set the current bucket to be nothing on start.
Have only one representation of the buckets in the scene.
Fix for the "jump to cursor/finger" problem.

Have only one currentBucket variable accross the BucketController and
GameScreen classes.
Refactoring. Simplifying the use the current bucket.