Polytope.from_box accepts list of lists

- if Polytope.from_box gets list of lists, it converts it numpy.ndarray
- plot single polytopes with random color and don't show them, because any show after the first is ineffective.
- update continuous examples to pass list of lists to from_box
- add example code to handle unrealizable spec in robot_continuous
doc: improve synth.synthesize
synth: shorter lines