Refactoring of visualization code

The visualization infrastructure in KnowRob had grown a lot over the past years and had partly become somewhat messy, so some refactoring was needed. In rev. 958, several changes have been merged back into trunk. If you are just using the packages mod_vis and knowrob_common, no changes should be necessary. If you direclty use the classes in these packages, you will likely need to update your name spaces and possibly the locations of .jar file references. A summary of the main changes: