sl/fixed_point: split into two modules

... to prevent unnecessary module dependencies
sl/fixed_point: basic object model [not tested]
sl/fixed_point: implement heap loading [not tested]
sl/fixed_point: implement finalizeFlow() [not tested]
sl/fixed_point: use the new object model for plotting
sl/fixed_point: implement createTraceEdges()
sl/fixed_point: implement detectContShapes()