Increase maximum number of classes to 10.

Maybe this should be a user-defined variable in the settings.
Clean up annotation panel code.
Remove unused code and set height of annotations panel to 1.

A new panel to contain the annotations panel needs to be created to prevent the border to go to the limits of the GUI.
Remove code (probably there by mistake).
Create container panel for the annotation panel so the border sticks to the components.
Remove unused imports.
Correct comment.

Class colors are not random but selected by golden angle.
Remove old commented code.
Add version to plugin's title.
Fix minimux size of the GUI to prevent strange behaviors when reducing the size of the window.
Add scroll panel for the label/annotation panel.

Useful when the number of classes is larger than 4.
Add javadoc comments.