Add self-contradiction filter panel

Added the self-contradiction filter panel to the SidebarPanel.
Self-contradiction panel: You can choose the desired statement-type, then the corresponding variables as well as the "agreement"-boolean. A Jtree will show the chosen variables for which a (self-)contradiction was found. By clicking on the statements involved, the statements are loaded from the documents.
TODO: Trimming and implementation of fail-safes needed.
Why is there not action in this and the next ItemListener? Either add something or remove the listeners.