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.
Are you sure that <String> should be removed? I think this is part of the generics definition of JComboBox starting with Java 7. Please use Java 7, not 6. See here: http://stackoverflow.com/questions/12821700/jcombobox-safety-type-difference-in-java-7-and-java-6