Add boxed means classification
Change initialization order in getCreateClassificationPanel
It's important to create the "Create" button before the combo box that
holds the classification methods as this combo refreshes the state of
the button according to its currently selected method.
Fix a bug when trying to remove a line while the selected element is not the key but the label
Merge pull request #473 from agueganno/boxed-means

Introduce boxed means classification