Correct bug on classic watershed transform.

Notice the difference between having the && or not.
Rename variable to prevent confusion with class name.
Remove empty lines.
Fix same bugs in the animation calculation.

Notice the difference using && in the condition and the name of the variable that was matching hte class name.
Merge branch 'master' of https://github.com/ijpb/ijpb-plugins
Add note in the javadoc comments to warn about the limitation of the watershed method from Soille & Vincent.