Add option to show all pareto-optimal solutions

[elKei24]

Like #26, but this time functioning 😆 When running the MiniBrassRunner with the parameter --pareto, it will not only output a single solution but all pareto-optimal solutions. The user of course should ensure that the variables are constrained enough in order for this to be feasible with reasonable resources.

While working on that feature, I refactored the MiniBrassRunner and split it into some smaller ones:

• WorkingModelManager cares about creating/updating/removing the working MiniZinc file(s)
• MiniBrassRunnerMain cares about parsing the command line parameters and then executes the MiniBrassRunner
• SingleUseMiniBrassRunner encapsulates stuff needed for a single execution but not afterwards (like the working model, …). It is immutable from outside, in contrast to the MiniBrassRunner using this class.

The example from #27 again highlights the usage and will output four solutions:

var 0..2: x;
var 0..2: y;
constraint x != y;
solve satisfy;

include "defs.mbr";

PVS: px = new WeightedCsp("px") {
	soft-constraint x0: 'x = 0';
	soft-constraint x1: 'x = 1';
	soft-constraint x2: 'x = 2' :: weights('2');
};

PVS: py = new WeightedCsp("py") {
	soft-constraint y0: 'y = 0';
	soft-constraint y1: 'y = 1';
	soft-constraint y2: 'y = 2' :: weights('2');
};

solve py pareto px;