Configurable algorithms

[istvank]

Whenever I call for example the DFG Frequency Visualizer, I get different node IDs in the resulting DOT. In my app, I use d3 to animate the resulting visualization, which works by diffing the last and the current DOT. With different IDs that does not work. I suggest adding an options object to FrequencyDfgGraphvizVisualizer in which we could specify whether we want to have static IDs (e.g., by hashing the label) or random ones.

For now, I changed https://github.com/pm4js/pm4js-core/blob/main/pm4js/visualization/dfg/frequency.js#L19 to a hash of the label.