Remove All button to clear the world of objects.
relayout buttons side by side
Fixed multi-threading issue (it was really difficult one to fix)
Even though lock/unlock (Mutex) protects the shared resource,
Swing's callLater() ended up creating a new thread within whose
context, the perspective for the ownership for the lock was different.
The code was written such that the lock is held by the caller, but
since the code passed to callLater() was going to execute in different
thread context, the lock/unlock() call didn't become symetric.
merged latest master
Merge branch 'mergebranch'
This include Edward's change and my change about ui.