Floating in Acumen

We have made progress towards making the current implementation of Acumen parametric over the type of real numbers. We have made the necessary changes in most of the functions that needed to be modified (functions dealing with GroundValues) and we have identified the classes that need to be made parametric. The key type is the type of GroundValues used in both the abstract syntax trees generated by the parser and in the values used by the interpreter. From the start it is the class AppModel that initiates parsing and interpretation. Results are then collected in a TraceModel and visualized with TraceView. Up to the TraceModel we will keep parametric types and functions, while in TraceView we have to fall back to Doubles in order to use Java's libraries for 2D-graphics.