Dynamically generated legend

[david-strahl]

• [x] coloring of classes, features and binary choice (included, voted, ...)
• [x] clear separation between classes and features using a pattern (striped, dotted, ...)
• [x] class and feature grouping (assigning the same color)

[david-strahl]

• [x] deletion
• [ ] don't mix class and features
• [x] color whole group
• [ ] overwrite labels in tree with group name (only when all have the same color)
• [x] scrolling in group and of all groups